Pascal Dihé

Ralf Denzer
email: ralf.denzer@enviromatics.org

Sascha Schlobinski

An Information Model for a Water Information Platform

Keywords: water information platform, water data model, spatial data infrastructure, spatial information platform

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction and Related Work

The re-use of publicly funded governmental data has received a lot of attention recently. In the environmental domain, it is clear that improved public services need exchange of data across governments at all levels. Governments keep producing information products at all levels, and some of them are more or less readily available.

Reporting obligations in the EC, for instance demanded by the Water Framework Directive (WFD) 1 , are direct inputs to European datasets. Water-related information is progressively made available on-line by a large variety of actors, including water data from operational monitoring and reporting of authorities. In Europe, the EEA plays an important role by providing water information through WISE and the water data centre2 . Data does not only include monitored or reported data but also fundamental information like basin networks [START_REF] Ecrins Eea | EEA Catchments and Rivers Network System, ECRINS v1.1[END_REF]. Over the past years, the Australian government has made large efforts in building water information platforms, information systems and tools [2]. Similarly, in the United States, CUASHI [3] acts as an alliance to improve water information and associated ICT. At interna-tional level the GEOSS data core also lists many water-related information resources [4].

However, on-line means different concepts to different people, from just presenting data to full service integration, with or without registration and authentication [START_REF] Denzer | An information platform fostering re-use of water data[END_REF], and re-use of data is not happening at large scale, and platforms, particularly those developed in R&D projects often do not survive long after the project. Recent discussions in the community [START_REF] Denzer | Hydroinformatics: Interoperability, standards and governance of water information infrastructures[END_REF] have identified a fundamental gap between concepts, research and implementation. This gap is given by a) a distance between the modelling community / modelling environments and infrastructure developers / providers, b) a lack of tools supporting the uptake of infrastructures being built and a lack of understanding, how "re-purposing" (re-use under different context) of data can be supported.

As part of the SWITCH-ON project, a Spatial Information Platform (SIP) is being developed, which supports the reuse of information products for the water science domain. This platform is used by water scientists and aims at integrating water related data from various sources including open government data. The re-use (re-purposing) of data is a central element of the platform. The concept of this SIP has been published recently [START_REF] Denzer | An information platform fostering re-use of water data[END_REF] and a first version is on-line3 .

The core platform is implemented with a stack of freely available open source software compiled in the CIDS product suite of CISMET GmbH. This software suite consists of a set of software components, application programming interfaces (APIs), management and development tools, services and applications, with a special focus on interactive solutions which need to integrate geo-spatial systems with databases, sensor networks, document-oriented systems, unstructured information sources and numerical models. CIDS is particularly suited for solutions which have to be built across existing heterogeneous information systems, which may be under control of different organizations. CIDS has been used in numerous projects since 1999. For recent projects see [START_REF] Denzer | How to build Climate-Change enabled EDSS[END_REF][START_REF] Hell | An Information System Supporting WFD Reporting[END_REF].

Platform Architecture

The architecture of the SIP is separated horizontally into three disparate layers: a GUI Layer (graphical user interface), a Service Layer and a Data Layer (figure 1). Each layer contains several components or sets of components. Interaction between components happens between components of adjacent layers. Apart from a few exceptions, GUI components, for example, do not communicate directly with the data repositories. These three layers are accompanied by a vertical Tools Layer.

Fig. 1. SIP architecture

The Data Layer is concerned with the storage and management of data and metadata (e.g. catalogue data). The most important component of the Data Layer is the Meta-Data Repository, a software component which is responsible for the storage and management of the meta-data compliant with the information model described in this article.

The Service Layer contains components that offer public service interfaces (APIs) which can be used by public and expert client components of the SIP. Those services also implement most of the (server-side) business logic of the SIP. They are supported by tools which provide additional functionality (e.g. data conversion) and which can be directly embedded in the respective service implementation.

The GUI layer of the SIP architecture contains user interface and user interaction components for expert and external users. External users include the general public which is able to use the public GUIs of the SIP without prior registration. Expert users have more access rights than external users, e.g. for the manipulation of data and meta-data.

The Tools Layer contains several supporting components that provide common or specialized functionality which are used by many different components of any other layer. Some tools are implemented as services and can be called from within other services and GUIs, while other tools represent algorithms or processes that can be embedded in services or (expert) GUIs. Some tools provide their own user interfaces.

Considerations About Standards and Information Models

The main purpose of the SIP information model is to support an extension of the common publish-find-bind pattern towards re-purposing of data (re-using data in a different context, see [START_REF] Denzer | Hydroinformatics: Interoperability, standards and governance of water information infrastructures[END_REF]). This extended pattern is publish, find, bind, transform (figure 2). As users re-use data, they not only include data in their analytics, they often also transform data into a new context or frame of reference.

Fig. 2. Extended pattern for re-purposing of data

Although widely adopted information models for the description of data and services exist (e.g. ISO19115 [START_REF]Geographic information/Geomatics[END_REF] and ISO 19119 [START_REF]Geographic information/Geomatics[END_REF]) the decision was taken that the information model for the water information platform should not be based on one of these standards alone. This is especially true for the requirement to consume and possibly to feed-back open data from existing catalogues. This leads to the imperative to support different (meta)data formats and standards which demand a flexible information modelling approach. Accordingly, the commitment to one (meta)data standard or profile may hinder external providers of open data that are compliant with the Standard Information Model to publish their open data to the SIP. Furthermore, support for the documentation of scientific analyses, the description of software (tools), aspects related to re-repurposing open data, inherent features for cataloguing, and other topics that have to be considered at the level of the information model, are only partially covered by existing (meta)data standards.

For instance, the commitment to one and only one (meta)data standard or profile could hinder external providers of open data to publish their open data or results of their studies to the SIP.

Open Data find bind transform publish

The design aim for the SIP was to support different (meta)data formats and standards in order to provide a flexible framework. This demands a flexible information modelling approach. Thus, instead of defining one fixed information model that is based on a selection of particular meta(data) standards or profiles, the information model for the SIP can be tailored to actual needs.

An interesting approach which goes in the same direction has been adopted by the federal German Open Data portal (GovData.de) [START_REF] Marienfeld | Metadata aggregation at GovData.de -An experience report[END_REF]. GovData's information model is based on a meta-data structure (domain model) developed by the Open Knowledge Foundation for the Comprehensive Knowledge Archive Network (CKAN) [START_REF]Comprehensive Knowledge Archive Network[END_REF]. CKAN is a de-facto standard for catalogues of Open Government Data (OGD). The CKAN domain model distinguishes between resources (e.g. data, services and tools) and their actual ("physical") representation (e.g. database, file, service endpoint, etc.). It defines a fixed set of mandatory or optional attributes to describe resources and their representations (title, description, license, contact, etc.) and allows the extension of the model by introducing arbitrary "extra attributes". GovData has made extensive use of this extension mechanism and created its own CKAN-based OGD meta-data schema [START_REF]Schema and documentation to be used by the German Open Data Portal[END_REF].

Furthermore, the CKAN domain model can be mapped to semantic-webcompatible standards like Dublin Core [14] and the Data Catalogue Vocabulary (DCAT) of the W3C [START_REF] Maali | Data Catalog Vocabulary (DCAT)[END_REF]. While at first glance CKAN seems like the ideal the candidate for the information model for the water information platform, one must consider that catalogue functionality, essentially providing access to a collection of datasets, is just one small part of the SIP. Furthermore, the SIP also has to interface with other types of catalogues like OGC Web Catalogue Service (CS-W) [START_REF]OpenGIS® Catalog Services Specification, Version 2.0[END_REF] to ensure that resources managed by the SIP can also be exposed in CS-W, among others. Nevertheless, the concepts of the CKAN domain model as well as support for meta(data) standards like Dublin Core, ISO 19115, etc., were considered in the design of the information model for the water information platform.

Platform Information Model

The design of the SIP information model follows a graduated approach with three different levels of increasing extensibility and flexibility: a relational model, dynamic tag extensions and dynamic content extensions.

The first layer is a relational information model (figure 3) which simultaneously defines the outline of the two subordinate layers. It is implemented as object relational database model of the CIDS platform and supports the core business processes of the SIP. Besides basic classes for resources, their relationships and representations, the model uses several categories from the ISO 19115 meta-data standard to define a set attributes needed to describe those classes. The relational model is also the basis for both the internal and external catalogues of the SIP. The most important classes of the relational model are

• Resource

Resources are the central entity of the information model and the catalogue. They logically describe a dataset, a service, a tool, etc. Resources have a set of core attributes that have been derived from the basic ISO 19915 metadata categories. Furthermore, arbitrary additional metadata can be associated with a resource.

• Representation

Among other roles, the representation defines how to actually access a particular instance of a logical resource. A resource may have different representations. For example, a dataset may be available in different spatial or temporal resolutions or different formats.

• Relationship

This class is used to specify relationships (e.g. "derived from") between resources, e.g. to track and document data transformations and processing (lineage) of resources. The type of the relationship can be identified by a respective tag and arbitrary additional meta-data can be associated with a relationship.

Fig. 3. Overview of relational model

• Metadata

The metadata class represents additional meta-data about a resource or a relationship in a structured or semi-structured format, for example meta-data on data quality.

• Tag and Taggroup

Tag and Taggroup represent the dynamic tag extension layer of the Standard Information Model. Taggroups define a general classification for tags and thus can be used to create lists of predefined tags (e.g. code lists).

Dynamic tag extensions provide the possibility to extend the information model for the water information platform without causing changes to the relational model itself. Accordingly, new information-needs of SIP client applications (external catalogues, tools, etc.) can quickly be fulfilled without the need to change the internal database structure of the Meta-Data Repository. Besides the possibility for extending the relational model by introducing new tag groups, tags and tag groups are mainly used to define fixed value lists like standardized topic categories, INSPIRE compliant keywords lists and so on.

Dynamic content extension is a simple mechanism for further extending the information model by either dynamically injecting arbitrary content encoded in plain text into the model or by providing references (URIs) to externally stored content.

Fig. 4. Dynamic Content Extension

In the relational model, dynamic content extensions are represented by triples of attributes "contentType", "contentLocation" and "content". The "content" attribute contains the actual content encoded in plain text, for example a JSON or XML document. Although this type of content is not directly part of the relational data base model, it can be used to store structured or semi structured information that can be processed by content-aware tools or clients. The attribute "contentLocation" defines the location of the content when the content is not dynamically injected but is referenced. The type of this attribute is a URI (RFC 3986).

The "contentType" attribute refers to standardised Internet Assigned Numbers Authority (IANA) media types (image/png, text/plain,...) as well as to custom industry standard media types (application/x-netcdf, application/gml+xml,...).

While the content type is in general sufficient to identify the data stored in the content field of the representation, a URL that is stored in the contentLocation field may however not directly point to actual data. Instead, the link may lead to an online form for accessing the data (in different formats) or a service endpoint. Therefore additional information about the handling, access and processing of content must be provided.

For this purpose, dynamic tag extensions can be used to introduce new tag groups like "function" and "protocol". "Function" defines for example the function that can be performed when following the "contentLocation" link to the resource representation. Examples of such functions may include "download" which enables the user to directly download the resource representation or "order" where the link value is an URL of a web application that requires user interaction to order/request access to the resource representation.

Classes of the relational model with support for dynamic content extension, and thus containing the three aforementioned attributes, are "Representation" and "Metadata". In the case "Representation", content is generally provided by reference. Thus the "contentLocation" attribute contains a URI that points to actual resource data.

Mapping to Related Standards

The SIP also has to interface with other types of catalogues like OGC Web Catalogue Service (CSW) or Open Knowledge Foundation for the Comprehensive Knowledge Archive Network (CKAN) catalogues. For this purpose, Published Catalogue Access APIs have been introduced which provide public and standards based access to metadata stored in the SIP meta data repositories.

Because OGC CSW is one of the most commonly used data catalogues, the open source CSW implementation pyCSW (which is the reference implementation of CSW) has been selected as one realization of a Published Catalogue Access API. Since pyCSW retrieves its complete data from a relational database model, a mapping of the relational model of the SIP to the Dublin Core encoding of CSW Core Metadata schema could also been defined.

This mapping is shown in figure 4. The tables represent an excerpt of the Dublin Core meta-data profile as adopted by the CSW standard. The boxes represent the respective tables of the data model. The connections represent the mapping.

Fig. 6. Potential provenance extension

This simple relationship (fromResource / toResource) can for example be used to describe the I/O of an experiment (model run), a script for repurposing, etc. The type of the relationship can be identified by a respective tag. Interestingly, arbitrary additional meta-data can be associated with a relationship. This is where the actual lineage meta-data, e.g. a link to the protocols of an experiment, or a description could be stored. These considerations are part of future work.

Fig. 5 .

 5 Fig. 5. Mapping to Dublin Core / CSW

  Since provenance of re-used data and modelling experiments is important, it should be considered also in the relational model of the SIP. Up to now provenance information has not yet been considered systematically in the project. The "Relationship" class can be used to describe the relationship (lineage) between resources and Dynamic content Extensions can be used to represent the actual lineage meta-data.

		Representation
	uuid
	name
	description
	tags [ ]
	contentType
	contentLocation
	content
		1...*
			Resource
			uuid
			name
			description
			tags [ ]
			spatialCoverage
		1	temporalCoverage creationDate
			publicationDate
			lastModificationDate
			contact
			license
			metadata [ ]
			representation [ ]
			2	1
			Contact
			name
			description
			organisation
			email url	Relationship
			name
			0...*	description
			tags [ ]
			fromResource
			toResource
			metadata [ ]
	6	Future Work

http://ec.europa.eu/environment/water/water-framework/index_en.html

http://www.eea.europa.eu/themes/water/dc

http://www.water-switch-on.eu/sip.html

Acknowledgements

The SWITCH-ON project is funded under the European Framework Program FP7 (contract number 603587).


Robert A Atkinson

Peter Taylor
email: peter.taylor@csiro.au

Geoffrey Squire

Nicholas J Car

Darren Smith

Mark Menzel

Joining the dots: using Linked Data to navigate between features and observational data

Keywords: linked data, spatial data infrastructure, spatial information platform, hydrological features

Information about localized phenomena may be represented in multiple ways. GIS systems may be used to record the spatial extent of the phenomena. Observations about the state of one or more properties of the phenomena are available from real-time sensors, models, or from archives. The relationships between these data sources, or specific features in different data products, cannot easily be specified. Additionally, features change over time, their representations use different spatial scales and different aspects of them are of concern to different stakeholders. This greatly increases the number of potential relationships between features. Thus, for a given feature we can expect that heterogeneous information systems will exist, holding different types of data related to that feature. We propose the use of Linked Data to describe the relationships between them. We demonstrate this in practice using the Australian Hydrologic Geospatial Fabric (Geofabric) feature dataset and observational data of varying forms, including time-series and discrete measurements. We describe how different resources, and different aspects and versions of them, can be discovered and accessed. A web client is described that can navigate between related resources, including using the Geofabric's feature relationships, to navigate from one observational dataset to another related by hydrological connectivity.

Introduction

An identifiable real world phenomenon within a spatial context, or a "feature", may be represented in many different information systems in different ways, for different purposes. A Geographical Information System (GIS) may be used to record the spatial extent of the phenomena, as defined or observed. Observations about the state of one or more properties of the phenomena, such as the height of a stream, may be available through real-time sensors, or from archives. Different systems may use different, but related, views of the phenomenon, characterized by different Feature Types and relations between them. For example, a river may have multiple views of its channel, connectivity, banks, cross-section etc. A "Domain Model" may be developed to describe these relationships, although each data representation is often structured in terms of a simplified "Product Model" that only describes a single viewpoint. Data representations are usually tied to these simplified Product Models, and currently they are not easily discovered or navigated using the relevant Domain Model. The relationships between data products, or between specific features in different data products, cannot easily be specified using the types of specialized systems in use.

Different information sources may be linked in a customized application that is configured to know the location and type of each available source. This may be by pre-loading data into a specific data store, or by consuming it from (web-based) services, with the semantics of each dataset understood and hard-coded directly within an application. This results in systems that hide valuable relationships between datasets, for example between specific features (e.g. rivers) and observations (e.g. height, flows, water quality). These applications tend to be single-purpose and inflexible.

Linked Data [START_REF] Bizer | Linked data-the story so far[END_REF] is an approach to standardize aspects of semantics and encoding in a Web-based environment. Linked Data does not standardize semantics or vocabularies, and the cost of standardizing access and format needs to be borne by the data provider. Links need to be embedded by data providers also, and no guidance as to the semantics of these links is directly provided by Linked Data.

"Domain models" standardize the semantics used in an individual domain, and describe the relationships that may exist between features. ISO19109 [START_REF]19109.3 Geographic information-Rules for application schema[END_REF] describes how domain models may be formalized using UML, which supports the generation of exchange schema using GML, and more recently using OWL semantics as described in ISO/DIS 19150-2 [START_REF]ISO/DIS 19150-2 Geographic information --Ontology --Part 2: Rules for developing ontologies in the Web Ontology Language (OWL)[END_REF] .

The Geofabric [START_REF] Meteorology | Australian Hydrological Geospatial Fabric (Geofabric)[END_REF] is an Australian spatial data product that describes a range of hydrological features from catchments to river networks. Individual data products describe data structures within a dataset of the Geofabric, not the relationships between datasets. HY_Features [START_REF] Atkinson | An international standard conceptual model for sharing references to hydrologic features[END_REF] is a candidate conceptual model for describing hydrological features and their relationships. The Geofabric is designed to have navigable relationships consistent with the HY_Features model. The question is how to make these relationships visible and usable in practice?

This paper describes how we have used Linked Data to describe how alternate data product representations and observational data may be linked to specific features. We show further how domain models can be used to standardize and document links between different features. We demonstrate this in practice using the example of the Geofabric dataset and a river flow rating observational dataset. We describe some example use cases where this capability brings significant data integration benefits.

System overview

We propose the use of Linked Data to describe the relationships between systems. Domain models standardize these relationships and provide common vocabularies for data description. We use standard Semantic Web vocabularies, including the Vocabulary of Interlinked Datasets (VoID) [START_REF]RDF Schema vocabulary[END_REF], RDF-Datacube [START_REF] W3c | The RDF Data Cube Vocabulary[END_REF] and SKOS [START_REF] Miles | SKOS: Simple Knowledge Organisation for the Web[END_REF] to describe datasets and cross-references between them. Inter-feature relationship discovery is provided as a service, so it is not necessary to embed every possible relationship as a link in every dataset.

Multiple "views" of a resource are made available from a resource URI, with each view corresponding to a specific data product. The syntax for this follows the Linked Data API [START_REF] Epimorphics | Elda: the linked-data API in Java[END_REF], extended to allow discovery of available views within a generalized framework for spatial data in a Linked Data context [START_REF] Atkinson | Spatial Identifier Reference Framework (SIRF)-A Case Study on How Spatial identifier data structures can be reorirnted to suit present and future technology needs[END_REF].

For example, persistent identifiers are created for specific catchments, e.g. 'http://environment.data.gov.au/water/id/catchment/110535'. A listing of available views for a resource is provided through a "_view=alternates" URL. E.g. http://environment.data.gov.au/water/id/catchment/110535?_view=alternates. Resolution of this URL follows the pattern [START_REF] Cyganiak | Cool URIs for the Semantic Web[END_REF] of using an HTTP redirect (303) to display the available named views (of which 'alternates' is one). Views provided for Geofabric features include:

─ SimpleFeatures: provides a Web Feature Service (WFS) Simple Features view, useful for accessing with GIS or spatially aware software; ─ ahgf:cartographic: a cartographic, image-based view of mapped streams for this feature; ─ ahgf:AHGFManmade: WFS query that returns anthropogenic features within a feature (e.g. damns within a catchment); ─ related: lists spatial features that are topologically related in some way to this feature. E.g. for catchments, this may contains references to upstream catchments, outflow nodes or a containing basin. ─ monitoringpoints: lists monitoring points that are contained within this feature.

Each resource listed through these calls behaves in the same way. This provides predictable behavior for navigating between resources.

The software architecture to support these functions is provided by a number of distributed services. An overview is shown in Fig. 1. The design shows the use of Sparqlify [START_REF]AKSW/Sparqlify[END_REF] to map identifiers and context of spatial features through to a RESTful API provided by ELDA [START_REF] Epimorphics | Elda: the linked-data API in Java[END_REF]. ELDA provides a means to expose APIs over SPARQL endpoints, simplifying access to RDF data. This is the mechanism for indexing the spatial features into a Linked Data representation.

Implementation

The Geofabric is published using a range of OGC web services, such as Web Feature Services (WFS) and Web Map Services (WMS). We use the VoID vocabulary to describe the available datasets, including descriptions of the data access endpoints. A void:Linkset describes relationships between hydrological features and monitoring points, described using WaterML2.0. This provides the data backbone allowing navigation between spatial features and monitoring points, which supports the following example use cases:

1. A user starts at a monitoring point to gain an understanding of the local hydrological conditions (e.g. local river gauge/flow conditions, channel shape etc.) and then wants to explore details of upstream conditions or the nature of the containing catchment. 2. A user interested in the national/state level, and wants to explore the hydrology of a particular catchment. This involves catchment level data, but also typically leads to more granular exploration such as river-based observations.

Using the views described in section 4, details for resources can be retrieved through requests against a resource URI. An example call flow for requesting details of a catchment is shown in Fig. 2.

URI

Fig. 2. Requesting alternate views of a resource URI

A screenshot of the prototype web client that makes use of the data and link rich environment is shown in Fig. 2. The workflow for the web client is as follows (numbers correspond to steps show in Fig. 2):

1. A user navigates a spatial overview showing all monitoring points within a basin.

She selects a monitoring point of interest, and identifies its unique URI reference. 2. The containing catchment (http://environment.data.gov.au/water/id/catchment/110741) is found by requesting the 'related' view using the monitoring point URI. (The 'related' view itself may be "well-known" or discovered via the 'alternates' view of the monitoring point.) 3. To get a visual representation of the catchment requires finding a suitable view.

For convenience, we have chosen to make default GIS views available using the special view name 'SimpleFeatures' however it is possible to interrogate the 'alternates' view to discover available views, which may be classified and annotated to support this discovery. In this case a WFS service is linked to the 'SimpleFeatures' view of the catchment. Invoking this view (e.g. for XML http://environment.data.gov.au/water/id/catchment/110535?_view=SimpleFeatures &_format=gml3) is used by the client to retrieve a GeoJSON representation and rendered in the client. 4. Additionally, the monitoring point location and containing river network views are also requested via 'SimpleFeatures' views and rendered on the same map. 5. Further context for the catchment, in terms of its hydrological relationships to other features, is requested using the 'related' view. These are shown in the table on the right of the image. In future work the prototype will support automated and userdriven navigation further into the Geofabric feature set. E.g. show up-stream catchment, outflow nodes etc.

Fig. 3. Web client screenshot

Access to individual features facilitates access to the relevant parts of the Geofabric, rather than having a flat image-based view of all the features (e.g. through rendering an image from a WMS). This allows enhanced visualisations to be created. For example, the stream network within the catchment is dynamically rendered according to the size of the stream segment and whether it is perennial (blue) or non-perennial (green).

The approach described here provides multiple benefits:

1. By exposing the semantics of feature relationships it is possible to identify how different resources relate to a given starting point. Each client application does not need to have an inbuilt model of each feature-type in advance, how feature-types have been implemented, or where to access them. These aspects are all discoverable by introspection of available views for a feature of interest. This reduces the cost of development as well as removing the reliability on highly specialized software, such as GIS desktop packages.

2. Data transfer is reduced, as users are not required to download large spatial contexts for processing on localized areas (e.g. downloading the whole Geofabric Surface Network data product for analysis on one catchment). 3. Other specialized data products and relationships can be added in a dynamic way, without expensive changes to software and infrastructure. 4. Multiple formats can be provided, suitable for different client platforms.

Related work

There is a vast body of work related to the principles of the various Internet based architectures exploited, including the World Wide Web, Semantic Web, Sensor Web, Linked Data and Spatial Data Infrastructures. This section focuses specifically on use of Linked Data for enabling hydrological and spatial data infrastructures.

Spatial Data Infrastructure (SDI) approaches [START_REF] Rajabifard | Spatial data infrastructures: concept, SDI hierarchy and future directions[END_REF] introduce standardized protocols and formats for delivering feature data. For example, under the INSPIRE legislation (EC 2007) EU member states will standardize the delivery of datasets via Web services, including hydrologic features [START_REF] Noy | Where to publish and find ontologies? A survey of ontology libraries[END_REF]. INSPIRE does not, however, specify how individual features may be referenced in a Web environment, or dictate that a single representation of a feature exists.

A candidate standard formalized model for hydrological feature definitions, HY_Features, provides a domain model for feature types and their relationships [START_REF] Atkinson | An international standard conceptual model for sharing references to hydrologic features[END_REF]. HY_Features is focused on the issue of object identity rather than sharing representations.

The UK Location Strategy [START_REF]Place Matters: The Location Strategy for the United Kingdom[END_REF] makes distinctions between identifiers, definitions, and "spatial objects" which implement representations. It provides a pattern for implementing Linked Data using alternative representation forms, provided the "thing" in question is reliably identified.

Janowicz et al. [START_REF] Janowicz | Semantic Enablement for Spatial Data Infrastructures[END_REF] outline the key challenges in bringing semantics to SDIs. They propose a semantic enablement layer that injects semantic annotation into responses from WFS, WMS, SOS or other OGC Web Services. Our approach varies slightly in that it does not modify service responses, but augments with semantics through exposing a SPARQL (and subsequent REST) interface for indexing. The approach outlined by Jones et al. [START_REF] Jones | Making the Web of Data Available Via Web Feature Services[END_REF] and Harvey et al. [START_REF] Harvey | Little Steps Towards Big Goals[END_REF] addresses a different challenge: serving RDF data using a WFS endpoint, thus making Linked Data available to existing GIS consumers.

Key challenges for next generation SDIs are identified by Adams and Gahegan [START_REF] Adams | Emerging data challenges for next-generation spatial data infrastructure[END_REF]. They propose a 'model space' concept that covers the complex dimensions of large scale data integration. Our work here primarily touches on the spatio-temporal, semantic and authority dimensions. Additionally Adams and Gahegan [19, p. 127] identify the representation of spatial features and sets of features as a key challenge. Our work proposes some potential next steps in this area.

Linking raster data to the Linked Data Web is explored by Scharrenbach et al. [START_REF] Scharrenbach | Linked Raster Data[END_REF]. Their approach of using semantics to describe contextual information for raster data is consistent with our work of indexing WMS calls with relevant spatial bounding box-es. This allows raster data to be included without resorting to encoding every pixel into RDF [20, p. 4].

Having observations of phenomena associated with features is important for understanding the context of an observation. WaterML2.0 part 1 [START_REF] Taylor | WaterML2. 0: development of an open standard for hydrological time-series data exchange[END_REF] and the proposed part 2 [START_REF] Taylor | An information model for exchanging hydrological rating tables[END_REF] provide standard information models for representing hydrological observational data. Using WaterML2.0 with HY_Features is conceptually consistent, but use cases have not been widely tested or implemented. This work brings these together with Linked Data.

Much recent work has investigated representation of observational and sensor data as Linked Data [START_REF] Janowicz | A restful proxy and data model for linked sensor data[END_REF]- [START_REF] Compton | The SSN ontology of the W3C semantic sensor network incubator group[END_REF]. Our work focuses on bridging between spatial features and monitoring points (the source of observations and sensor data); the representation of observational data as Linked Data is not tackled, rather we describe existing data sets using Linked Data.

Discussion

We propose linking directly from a view of a feature to relevant related information using the approach described offers advantages to the current alternatives. There are two existing options: Having all links hard-coded into each feature (document-centric Web architecture) or using a catalog of datasets and services (service oriented architecture).

We can dismiss a document-centric approach for several reasons:

• it places all the burden on knowing what data is related on the original source dataset; • these relationships need to be expressed in a standard way that both data provider and client understand; • all possible relationships need to be encoded in the document (which may be large and costly to produce); • the approach does not scale to large datasets, or dynamic numerical models or sensors producing data not known in advance;

For a catalog-centric approach the best case is a data catalog coupled with a service catalog describing access points to services providing each specific dataset. This approach is fraught with challenges, especially the very high burden it places on the client to know:

• The location of a relevant dataset catalog service;

• How the catalog is organized (i.e. keywords it can be searched on);

• The catalog access protocol;

• The response format and content;

• Which services it can utilize for the task in hand, using the descriptions provided.

• How to install and configure specific software able to interpret the spatial or observational data.

Even if relevant catalogs can be found, there is still no standard way to describe exactly how features in different datasets relate, or how to invoke a service to access a view for a particular feature. The Linked Data API implementation described here utilizes URI resolution to perform all these roles seamlessly; all the client needs to do is to choose a view that it can understand.

Conclusion

Distributed heterogeneous data sources are a necessary reality in the case of widespread phenomena with multiple stakeholder perspectives, such as is the case with water resource monitoring. Using traditional dataset centric approaches to cataloguing, one quickly runs into a lack of a canonical means to describe relationships between features. We show how we can exploit domain models to standardize such relationships, then implement and utilize them for individual feature instances in a Linked Data environment. This approach avoids placing the burden on data providers to realize every possible link, or to transform existing data into a new Linked Data format. This approach results in easily discoverable data sources that can be used without significant data management overheads and specific software availability. The use of both Linked Data services and data-specific services (e.g. WFS, observational services) provide a less abrupt transition into the Linked Data world and ensures that well-established access patterns are reused.

Fig. 1 .

 1 Fig. 1. Architecture Overview

Resolution Persistent Identifier Serv ice (PID) ELDA

		Client
	E.g. 'alternates' view
		"related" view
	ResourceList	Lookup
		Related	E.g. mapPreview view
		SPARQL	E.g. SimpleFeatures view
	SPARQL
		Sparqlify
	Triple store		Web Feature Service (WFS)	Web Mapping Service (WMS)
	(Sesame)
			PostgreSQL DB

adfa, p. 1, 2011. © Springer-Verlag Berlin Heidelberg 2011

Acknowledgements

This work is part of the water information research and development alliance between CSIRO's Water for a Healthy Country Flagship and the Bureau of Meteorology. The authors would like to thank Simon Cox for his thorough review and assistance, and the anonymous reviewers for their suggestions.


Poets' Tombs and Conceptions of Poetry in Ancient Greece"

Tombs, in general, exist to maintain memory of the dead. Their function is to preserve an image of the deceased, either with the words of an epitaph or with a portrait of the dead. But what makes a tomb suitable to be the tomb of a poet? What kind of σῆµα or epitaph fits a poet? As we shall see by reviewing the traditions about the tombs of Homer, Hesiod, Archilochus, Stesichorus, Simonides, Pindarus, Aeschylus, Sophocles and Euripides, there are several ways to answer these questions.

The present study focuses on ancient testimonies about the tombs of Archaic and Classical poets and/or remains of their monuments, in order to see if they refer to the poetic talent of the deceased. 1 The main sources are the ancient biographies, called Lives, of the poets, but other texts likewise mention these tombs. We also possess remains of a tomb of Archilochus, inscribed more than a century after his death. Obviously, locations, shapes of monuments or epitaphs cannot describe at length the art of the deceased. By their nature, they imply fragmentary and selective information. But the selection itself informs us about the particular features that are considered worthy of memory, because they are able to define the dead's identity. Some words, acts or decorations have undoubtedly been chosen by their author to commemorate the poetic status of the dead. By contrast, others might suggest poetry to the reader or viewer even if it wasn't their original purpose. They shall nonetheless be included in our survey, because they can shed new light on the evolution of poetic reception through the centuries. Indeed, writing a poetic biography or erecting a monument for a poet is a first step in reception, but the biographical texts and material culture are open to different readings, as is attested by modern studies. On the other hand, these pages shall account only for testimonies that appear of some relevance for the present investigation, because the idea is to highlight some tendencies and chronological evolutions in the conceptions of poets, which require an overview of several cases. Thus, the sepulchral epigrams that are conserved in Greek Anthologies will be set aside, unless they are also "the" epitaph transmitted by the rest of the tradition, because these poems are meant to convey metapoetic statements, which are specific to that genre.

We shall suggest that, among all the factors determining the tradition about poets' tombs, the conception of the poetic genre to which the poets were thought to belong played a growing role through the ages. This phenomenon is very likely to be linked to the emergence of the idea of poetic genres during the 5 th century BC and its fulfilment in Alexandrian criticism. 2 As a matter of fact, the selection of a few authors as perfect illustrations of one genre caused a "specialisation" of each poet, as a representative of one genre only and, inside that genre, of particular traits.

Epic poets: Homer and Hesiod

No antique remains of Homer's or Hesiod's tombs survive, but the ancient texts refer to the monuments quite often. The biographical narratives about the two poets have long been proven to rely on Archaic spoken traditions. 3 We shouldn't expect, then, that features of epic 1 Εditions and translations quoted from Loeb Classical Library: Homeric texts and testimonia, Certamen:

as a poetic genre shape the whole tradition concerning their tombs. As a matter of fact, they don't, but certain details, maybe of later date, do hint at epic as a genre.

Homer is supposed to have died on the island of Ios, but very few information about his tomb is given in the Ancient sources. The texts only state that he was buried near the sea, "on the very sea-shore", αὐτοῦ ἐπ' ἀκτῆς, according to the pseudo-Herodotus, whose biography is dated to the 2 nd century AD. 4 Even if this statement is likely to be a topos related to the fact that Homer is presumed to have been buried on an island, 5 the location of the tomb may allude in the reader's mind to the important place of the sea in the Odyssey and Iliad, where the sea-shore is precisely connected with grief, sorrow, and the idea of death (above all Patroclus' death and Achilles' foretold death). 6 So it is appropriate to the poet, probably perceived as the composer of those two poems since the first half of the 4 th century BC. 7 Nevertheless, this detail does not define him as a poet, and surely not as an epic poet. But the Lives add that the following epigram was inscribed on his monument:

ἐνθάδε τὴν ἱερὰν κεφαλὴν κατὰ γαῖα καλύπτει, ἀνδρῶν ἡρώων κοσμήτορα, θεῖον Ὅμηρον. 8 This poem is connected to Homeric poetry in many ways: it rewrites several Homeric verses; 9 it depicts Homer as a poet of heroic poetry; it gives the poet a sacred status, traditionally connected by Ancient authors to poetic divine inspiration, which seemed implied by the preliminary invocations to the Muses in both Iliad and Odyssey. The use of hexameter as well as reference to heroes point to epic as a genre. In fact, the ancient texts that are interested in the origins of epic poetry frequently use these two criteria as the defining components of epic. 10 Thus, this is not the shape (which we know nothing about) or the location of the tomb that commemorates Homer as an epic poet, but the supposed inscription of the monument. The function of the epitaph as a reminder of the dead's identity makes it logical. Some sources add that Homer composed this as his own epitaph before dying, which implies that these verses express a self-definition. On this matter, we shall note that pseudo-Herodotus raises against this definition of the dead, particularly as being a self-definition. He affirms that the epigram "was inscribed by the people of Ios at a much later date, after his poetry had spread abroad and become universally admired -it is not by Homer himself". 11 This controversy is relevant to our study, because it could attest that the conception of the poet appearing in the epigram doesn't seem genuine to the writer of the Vita attributed to Herodotus. In fact, it is very different from the image given by the rest of Homer's ancient biographies, especially the Vita Herodoti, where Homer is more modelled on bards, rhapsodes and sophists than on epic poet. 12 The references to Hesiod's poet status in the stories about his burial near Naupactus and the removal of his remains by the inhabitants of Orchomenus, who were said to have later transferred them to their city, 13 seem at first glance even less clear than for Homer. They are mostly shaped, as shown first by Angelo Brelich, after heroic myths, transferred and adapted to the poet. 14 But Natasha Bernashdy persuasively argued that some details of the tradition were likely to be related to the content of two passages of the Works and Days. 15 More generally, the location of Hesiod's first tomb in the sacred precinct of the Nemean Zeus could have been easily associated in the reader's mind with the general scope of the Works and Days, which advise to take good care of one's farm and to observe the Justice of Zeus. The epiclesis "Nemean" alludes both to pasture and justice/revenge (nemesis). The supposed epitaph of the first tomb has not come down to us, but we know of at least one epitaph of the second tomb, which has been, according to Tzetzes, erected for Hesiod in Orchomenus' agora. 16 The epitaph reported by several ancient authors, mostly attributed to Mnasalces, is the following:

Ἄσκρη μὲν πατρὶς πολυλήιος, ἀλλὰ θανόντος ὀστέα πληξίππων γῆ Μινυὰς κατέχει Ἡσιόδου, τοῦ πλεῖστον ἐν ἀνθρώποις κλέος ἐστὶν ἀνδρῶν κρινομένων ἐν βασάνῳ σοφίης. 17 The qualification of Ascra as πολυλήιος, "with many cornfields", undoubtedly reminds us of Hesiod's agricultural advice in the Works and Days. The second part of the epitaph echoes both several verses of Archaic poetry and another epigram attributed to Pindar whose content has been demonstrated to point to the 5 th century BC: 18 χαῖρε δὶς ἡβήσας καὶ δὶς τάφου ἀντιβολήσας, Ἡσίοδ', ἀνθρώποις μέτρον ἔχων σοφίης. 19 The use of both terms metron and sophiê -particularly together -hints at a figure of poet. Sophiê is the quality commonly claimed by and credited to Archaic poets. As Andrew Ford has underlined, the word metron is ambiguous in the Classical period: it means "measure", as a moral term and a metrical notion. 20 The term may even allude to the posture of the poetic voice of the Works and Days, who preached observing metra. 21 In Mnasalces' epigram, the reference to sophiê, linked to the allusion to the Works and Days, seems to highlight Hesiod's status as a didactic poet. We shall note that all the elements alluding to Hesiodic poetry in the 13 Burial near Naupactus: Paus. 9.38.3, Certamen 14; in the precinct of Nemean Zeus: Plut. Mor. 162e, Tz Vita Hesiodi. Bones transferal to Orchomenus: Paus. 9.38.3-4, Plut. Mor. 162e, Certamen 14, Procl. ad Hes.Op. 631, Tz Vita Hesiodi. Texts and commentary in Kimmel-Clauzet (2013), 321-326 and 135-141. 14 Brelich (1958), 320-322. 15 Bernashdy (2011). The author supposes that cults of Hesiod in Oinoe and Orchomenos impacted the very text of the Works and Days. The lack of evidence for cults including festival with recitation of Hesiodic poetry in both places makes this impossible to prove. It might be only that, as often, the text of the Works and Days inspired parts of the biographical tradition about the poet. 16 We don't know anything about the shape of the tomb. Many modern critics assume that Hesiod's tomb was in Minyas' tholos, but Pausanias' report of Orchomenus' monuments (9.38.1-10) only states that there was a tomb of Hesiod in Orchomenos, not that it was in the tholos, and the way he describes the marvellous tholos in contrast to the usual denominations of taphos/mnèma used for Hesiod's tomb let us rather think that Hesiod's tomb was not in the tholos. On this question, see Kimmel-Clauzet (2013), 140-141. 17 "Ascra, the rich cornland, was my homeland, but now that I have died the land of the horse-smiting Minyan holds my bones, Hesiod's, whose glory among human beings is the greatest when men are judged in the trials of wisdom." 18 Kimmel-Clauzet (2013), 167-168. 19 "Hail, you who twice were young and twice received a tomb, Hesiod, you who hold the measure of wisdom for human beings." 20 Ford (2002), 18-20. 21 Hes. Op., 694: μέτρα φυλάσσεσθαι• καιρὸς δ' ἐπὶ πᾶσιν ἄριστος. "Bear in mind measures; rightness is the best in all things." traditions surrounding both Hesiod's tombs seem to refer to the Works and Days, the only poem that was unanimously thought to have been composed by him, according to Pausanias. 22 Thus, even if allusions to the specific type of poetry composed are minor,23 the two poets considered as the best performers of Archaic epic are each given their own distinct kind of epic: heroic epic for Homer, didactic epic for Hesiod, which are precisely the kinds of poetry attributed to both of them by the Alexandrians.24

Iambic Poet: Archilochus

The biographical tradition about Archilochus is strikingly affected by his status as an iambic poet, iambic poetry being generally identified in ancient texts with vituperation and obscenity and being therefore a source of criticism against Archilochus. 25 By contrast to this tradition, the inscription on the 6 th century BC capital discovered in Paros in 1961, bearing an epitaph for the poet dated to the 4 th century BC, does not mention his poetry:

̓ Αρχίλοχος Πάριος Τελεσικλέος ἐνθάδε κεῖται, τõ Δόκιμος μνημῆιον ὁ Νεοκρέωντος τόδ' ἔθηκεν.26 This is the most common kind of epitaph, apart from the mention of his origin, which is unusual for a man buried in his own country. Yet it is easily explained here by the honorific function of the monument. Neither the epitaph nor the capital can belong to the genuine tomb of Archilochus. The design of the monument, an ionic column, most likely surmounted by a sphinx, maybe included in an open-air doric temple,27 is clearly heroic (as might be the use of sole hexameter). This confirms the honorific function of the monument, but does not refer to iambic poetry, or to poetry of any kind.

By contrast, if we accept Anne Ohnesorg's hypothesis that this grave was in the 3 rd century BC included in the new Archilocheion, a sanctuary dedicated to the poet, where he was honored with the gods, we shall note that the inscriptions preserved on several orthostates belonging to the sanctuary, dating to the 3 rd and 1 st century BC, deal at length with Archilochus' poetry. 28 The poet's representation in these inscriptions is complex. Since it is not certain that they belong to a funerary complex, only an overview of the key elements shall be given here. In Mnesiepes' inscription, as shown by Andrea Rotstein, Archilochus is depicted as an iambic poet, but the inscription promotes a positive view of "mockery" rather than invective, and the obscenity is legitimated by a cultic context. 29 Sosthenes' inscription displays another kind of re-appraisal of iambos, by making it essential to the commemoration of the history of Paros and his citizens' bravery. 30 Contrary to Dokimos' epigram, which ignores -perhaps chooses to ignore? -Archilochus' poetry, Mnesiepes' and Sosthenes' inscriptions both try to recreate an image of the poet that does not suffer from his bad reputation as iambic poet, by recreating the genre itself. It is obvious these later authors cannot choose to ignore Archilochus' iambic poetry when he has become the most important representative of the genre for the critics. 31 Furthermore, the writing of Mnesiepes' inscription, which imitates a papyrus, reveals its ambition to respond to literary traditions. 32 Lyric Poets: Stesichorus, Simonides and Pindar 6 th and 5 th century BC lyric poets' tombs appear to be mainly thought as mirroring the kind of poetry composed by the dead poet. Even the very location or design of some tombs, at least for non-genuine monuments, has been impacted by the reception of the poetry composed. The testimonies conserved allow us to compare the case of three canonical poets: 33 Stesichorus, Simonides and Pindar. As we shall see, the traditions conserved about their tombs amazingly show a distribution of the poets as illustrations of different features of lyric poetry.

Stesichorus enjoyed an original tomb, which "had eight pillars, eight steps and eight corners", ὀκτὼ κίονας, καὶ ὀκτὼ βαθμοὺς, καὶ ὀκτὼ γωνίας, according to the lexicographers, who refer this to the proverb "πάντα ὀκτώ". Photius and the Suda add that the tomb was located in front of a gate named Stesichorean after the poet. 34 This implies that the whole area was devoted to sumptuous commemoration of the poet, and, what is more, that the supposed personality of Stesichorus gave the place its identity. 35 In these circumstances, we are allowed to presume that the opposite is also true, and that the original octogonal monument has something to say about the identity of the dead. The earliest source on the design of Stesichorus' monument is Zenobius, 36 who was in activity around the mid 2 nd century AD. He was surely relying on earlier sources, but they might be at best Hellenistic, as octogonal monuments seem to have been used in funerary architecture only since the Hellenistic period. 37 This monument is, thus, very unlikely to have been the genuine tomb of the poet. Two relevant parallels are an octogonal structure called the Octagon, which was located in the center of ancient Ephesus and dated to the second half of the 1 st century BC, and a monument located near the Porta Gemina of Pola in Croatia, dated at the latest to the first quarter of the 1 st century AD. The first structure was a monumental tomb, maybe of Ptolemy Arsinoe IV. 38 The latter was also for funerary use, but, according to Pierre Gros, it may have been used more for commemorative purposes than for an actual burial, e.g. by sheltering the statues of several dead. 39 That characteristic brings it closer to the Stesichorean monument. As to the design of the "tomb", Silvia Barbantani, who thoroughly studied the tradition about the Stesichorean octagon, persuasively argued that the octogonal shape of the 31 Rotstein (2010), 281-318. 32 Kontoleon (1955), 36-39. 33 On the canon of lyric poets, see Pfeiffer (1968), 203-207 and Barbantani (2010), 1-2 with further bibliography. 34 Phot. Lex. s.v. πάντα ὀκτώ: οἱ μὲν Στησίχορον φασὶν ἐν Κατάνηι ταφῆναι πολυτελῶς πρὸς ταῖς ἀπ' αὐτοῦ Στησιχορείοις πύλαις λεγομέναις. "Some say that Stesichorus was given an expensive burial at Catana near the gates called Steichorean after him". Suda s.v. Στησίχορος: αὐτὸν ἐλθεῖν φασιν εἰς Κατάνην κἀκεῖ τελευτῆσαι καὶ ταφῆναι πρὸ τῆς πύλης, ἥτις ἐξ αὐτοῦ Στησιχόρειος προσηγόρευται. "they say that […] he came to Catana and that he died there and was buried in front of the gate which is called Stesichorean after him." 35 Lots of monuments were named after poets, e.g. Homereion, Archilocheion, Mimnermeion… on this use of the poets' names, see Kimmel-Clauzet (2013), 190-192. 36 Cent. 5.78. 37 On the dating of the monument, see also Lefkowitz (2012), 169 n. 54. 38 On the Octagon of Ephesus, see Thür (2004). 39 Gros (2001), 412. On the Octagon of Pola, see Fischer (1996), 143-158 and plates 38-40. monument -and especially the reference to the number eight -was related to "Hellenistic Pythagorean theories" about "harmony of the universe", "identified by Pythagoreans with the musical and mathematical systems that shape the world". 40 Hence, the Pythagorean idea of musical harmony could have been applied to the poetry of Stesichorus. In fact, several other features of Stesichorus' biography are obviously influenced by Pythagorism. 41 One might wonder if this original design was also likely to be associated with the image of a cyclic chorus, in accordance to Stesichorus' image as first founder of choruses 42 , since an octagon fits perfectly in a circle 43 while giving specific places to stand, but the lack of evidence forces us to leave the question open.

According to Callimachus, followed by the Suda, whose article on Simonides quotes and comments on Callimachus' poem, 44 Simonides was buried in Acragas. His tomb was later destroyed by a General during a war, and used for the defence of the town. The passage of Callimachus' Aitia is not fully preserved, but the Suda gives us the end of the story: the city was taken by the very place where the tomb used to be located. 45 The words opening Callimachus' poem, referring to Camarina's destiny, allow us to think that he referred to the same fate. 46 Moreover, both texts show that the profanation of Simonides' tomb is the sin punished by the fall of the city, by linking this story with the well-known tale of Simonides' revenge by the Dioscuri at Skopas' banquet. 47 Callimachus underlines the parallel between the respect that the General ought to have towards the poet (identified by his epitaph) and the fear he should feel for the Dioscuri, who already helped him during his lifetime, by using a οὐδέ… Camarina would be such a threatening disaster as the removal of the tomb of a holy man." The inhabitants of Camarina had dried a lake near their city, without listening to the oracle of Apollo, who foretold them not to do so, and while they were later besieged, the attackers captured the city by passing through the way that used to be the lake (Serv. A. 3. 701). 47 The main sources for this tale are Cic. De orat. 2.86.351-3 and Quint. Inst. 11.2.11-16. For a record of other sources see Campbell (1991), 379. On this story, see Slater (1972).

ὤλισθεν μεγάλους οἶκος ἐπὶ Σκοπάδας. 48 The Suda's article shows a ring composition that refers to the best known tale at the beginning and end, and tells the profanation of Simonides' tomb in the middle. This story is thus supposed to receive its meaning by constant comparison with the other episode. It seems that the sacredness of Simonides, referred to as an ἀνὴρ ὅσιος at the beginning of Callimachus' poem, is due less to his status as host than to the fact that he sang of the gods and heroes. 49 The tomb, then, in accordance with the rest of Simonides' most famous biographical episodes, characterizes Simonides' poetry as praise poetry, and refers more precisely to a feature of victory odes that seemed to have disconcerted the ancient scholars: the importance of the mythological part. 50 Yet, another important aspect of Simonides' poetry, as already noticed by several commentators, is also present in Callimachus' aition: the epigrammatic composition. Callimachus chooses to preserve the lost inscription of the monument, by quoting it -or perhaps rather inventing it. 51 By doing so, he also recalls Simonides' status as paragon of epigrammatic poetry, which was attested at that time by the many epigrams attributed to him and apophtegmatic tradition, and was in competition with his standing as a lyric poet.

Quite surprisingly, no indication is conserved in the Lives of Pindar about his tomb or epitaph. The only -but fundamental -information is given by Pausanias. Visiting Thebes around 170 AD, he reports that Pindar's tomb is located on the race-course. 52 The location of the monument is without doubt linked to the poetry composed by Pindar. It recalls Pindar's role as poet of victory odes, particularly odes to winners of races, which were the most prestigious trial of panhellenic games. The monument commemorates Pindar as a poet, but of only one type of poems: the epinician. We cannot be sure that the monument seen by Pausanias is the genuine tomb of Pindar, 53 hence, it would be audacious to affirm that this selection goes back to Pindar's death. But it is certainly earlier than the selective school Choice of the end of the 2 nd century AD, which conserved only the four books of epinicians that have come down to us. It is striking that these poems, considered sufficient in preserving the poet's memory within his monument, are also the poems selected in the Choice. This consistency is even more remarkable when one recalls that this is clearly not the main concern of other monuments related to Pindar or of Pindar's Lives. Indeed, when Pausanias visits Thebes, he can see three dedications attributed to Pindar: statues of the Mother of Dindymon, Hermes Agoraios, and Ammon. 54 These statues remind the visitor of Pindar's role as a religious poet. So too might have the remains of Pindar's house, spared by Alexander because 48 "and he built my tombstone into a tower and showed no respect for the inscription, which declared that I, son of Leoprepes, lay there, the holy man of Ceos, who (knew?) rare things and was the first to devise a system of memory; nor did he fear you, Polydeuces and your brother, who once got me alone of the banqueters outside the hall which was about to collapse, when alas! the house of Crannon fell upon the mighty Scopads." 49 This is a recurring feature of poets' personae, cf. Kimmel-Clauzet (2013), especially 58-59, 198-199, 261-264 and 278-279. 50 See for exemple the idea of Simonides "accustomed to use digressions", παρεκβάσεσι χρῆσθαι εἴωθε (Schol. Pind. Nem. 4. 60b). The same kind of commentaries can also be found about Pindar, see Young (1964). 51 So Barbantani (2010), 47-48. She wonders if the reconstruction of the epitaph is only με Λεωπρέπεος κεῖσθαι Κήϊον ἄνδρα τὸν ἱερόν, "a very simple prose inscription in the archaic style" or includes τὰ περισσά and µνήµην (p. 50). I consider, with Durbec (2006), 73 n. 212, that the epitaph is supposed to include ὃς τὰ περισσά ..καὶ] µ̣ νήµην πρῶτος ὃς ἐφρασάμην, as the syntax suggests. It highlights Simonides' most famous achievement, as usual in literary sepulchral epigrams, which supports the idea of a Hellenistic forgery. 52 Paus. 9.23.2. 53 On the problematic datation of the monument, see Kimmel-Clauzet (2013), 146-148. 54 Paus. 9.25.3 (Mother); 9.17.2 (Hermes); 9.16.1 (Ammon). About Pindar's representation as founder of the cult of the Mother of the Gods, see Kimmel-Clauzet (2013), 233-235. of his quasi-religious respect towards the poet. 55 This aspect appears to be the dominant feature of Pindar's Lives too, where he is, above all, a poet of hymns, paeans and dithyrambs. The biographers aim to show how, at every stage of his life, Pindar can be defined as a man loved by the gods because of all the poems he composed for them. 56 What can explain, then, the discrepancy between the general image of the poet in the Lives and the representation given by his tomb? It might be due to their noncontemporaneous creation, but, since it is as difficult to date the content of the Lives as Pindar's monuments, we ought to leave the question open.

A last interesting document is a fragmentary declamatio attributed to Libanios, which states that Pindar has been killed by stoning and left without burial by the inhabitants of Thebes because he composed a poem in praise of Athens, which was considered a betrayal toward Thebes. 57 Even in an imaginary discourse -but which can be proven to play with the biographical tradition 58 -the treatment of the dead Pindar in late Antiquity is modelled on the reception of his work.

As we can see, different features of lyric poetry are emphasized for each poet: music and harmony for Stesichorus, specific genres of lyric poetry for Simonides (epinicians and epigrams) and Pindar (epinicians only). And even when they refer to the same poetic genres, the traditions surrounding the monuments -or the monuments themselves -hint at various aspects of the genre: the important place devoted to gods and heroes in victory odes for Simonides, the glory of praising racing winners for Pindar.

Tragic Poets: Aeschylus, Sophocles and Euripides

The traditions surrounding 5 th century BC tragic poets are also modelled on the reception of their practice of tragedy. The whole content of their Lives is even more influenced by ideas of tragedy as a genre and each poet's contribution to that genre than was the case for lyric poets, because their Lives appear to have been written together at an earlier stage of their development. 59 In this context, the testimonies about the poet's tombs are so regularly part of this representation that some of them have been, already in Antiquity, judged as disappointing. These judgments may be misleading.

Aeschylus' Life states that the poet was magnificently buried by the people of Gela in Sicily, where he was staying when he died. We are ignorant of the shape or precise location of the tomb, but are told that "all who made their living in the tragic theatre went to his tomb to offer sacrifices (ἐνήγιζόν) and recited their plays there". 60 The use of the verb ἐνήγιζόν highlights the heroic status attributed to Aeschylus in the Vita, 61 but his worshippers are limited to professionals of tragedy. The offering, the performance of tragedies, is also specific to a tragic poet. By contrast, the epitaph transmitted by the tradition surprised Pausanias and Athenaeus because it didn't mention Aeschylus' achievements as a poet, but only his bravery as soldier during the Persian Wars. 62 Their surprise is increased by the fact that they consider Aeschylus himself to be the author of the epitaph, and find difficult to accept that the poet preferred to recall his martial exploits over his poetry, especially considering his poetic fame. 55 On the quasi-religious respect expressed towards Pindar's house by Alexander according to ancient sources, see Kimmel-Clauzet (2013), 230-233. 56 On the representation of Pindar as θεοφιλής see Kimmel-Clauzet (2013), 63-69. 57 Lib. fr. 49 γ´, 3-4 Foerster. 58 Kimmel-Clauzet (2013), 69-72. 59 Hanink (2010), 54. 60 εἰς τὸ μνῆμα δὲ φοιτῶντες ὅσοις ἐν τραγῳδίαις ἦν ὁ βίος ἐνήγιζόν τε καὶ τὰ δράματα ὑπεκρίνοντο (Vita 11). 61 Ekroth (2002), 74-128. 62 Paus. 1.14.5; Ath. 14.23, 627d. On these texts, see Kimmel-Clauzet (2013), 169-170.

The absence of explicit reference to Aeschylus' poetry in his epitaph has always been noted and even considered a proof of authenticity, on the supposition that the soldier's bravery was more glorious during the Classical period than the gift of poetry. 63 But what if this epitaph was a commemoration of Aeschylus' poetry as much as his bravery? The end of the poem reads as follows:

ἀλκὴν δ' Εὐδόκιμον Μαραθώνιον ἄλσος ἂν εἴποι καὶ βαθυχαιτήεις Μῆδος ἐπιστάμενος. 64 Inevitably, it reminds the reader not only of the Persian War, but also of the Persians, a tragedy that had a great success both in Athens (winning the Dionysia in 472 BC) and Sicily, where Aeschylus, according to the Vita, "put on" the play "at Hieron's request and was highly praised for it". 65 The Persians' representation as barbarians in Aeschylus' tragedy is in accordance with the lapidary expression of the last verse, βαθυχαιτήεις Μῆδος. 66 Furthermore, the compound adjective βαθυχαιτήεις imitates a peculiar feature of Aeschylus' style, as Aristophanes mocks it in the Frogs, 67 where Aeschylus is depicted as priding himself on having composed The Persians. 68 It would, then, have seemed natural for ancient writers and readers to picture him alluding both to his own bravery and to this specific play in his epitaph.

All the traditions concerning Sophocles' burial and tombs depict him not only as a poet, but as the finest tragic poet that ever lived. The most complete source available to us is the poet's Life, which states that Dionysos himself intervened with Lysander in order to allow the funeral to take place. 69 The decoration of the tomb, a Siren, is -exceptionallymentioned. 70 The Siren as a funerary decoration was not uncommon in Sophocles' time, 71 but it becomes undoubtedly more meaningful when figured on Sophocles' tomb, as attested by Pausanias' version of Sophocles' burial, where the poet is himself called "the new Siren", τὴν Σειρῆνα τὴν νέαν, and is recognised by Lysander by this very appellation. 72 Pausanias comments: "down to the present day men are wont to liken to a Siren whatever is charming in both poetry and prose". 73 The epitaph of the poet transmitted in the Life goes further in 63 Pfohl (1967), 26;Sommerstein (1995Sommerstein ( -1996), 111-117. 64 ), 111-117. 64 "The famous grove of Marathon could tell of his courage and the long-haired Mede knew it well" (Vita 11). 65 Φασὶν ὑπὸ Ἱέρωνος ἀξιωθέντα ἀναδιδάξαι τοὺς Πέρσας ἐν Σικελίᾳ καὶ λίαν εὐδοκιµεῖν (Vita 18). The same indication is found in the scholia to Ar. Ran. 1028 with a reference to Eratosthenes' work On Comedy. 66 There is no reference to long hair in the play, but to thick beard (v. 316). Yet the play ends with the old men's Chorus mourning and tearing their hair. The image of the Persian with thick or long hair, as Sommerstein (1995-1996, 113) has shown, matches the iconography. It is also very likely to have become a topos of the Persians' representation during the Classical period, since Herodotus reports an oracle addressed to the Milesians using the sole substantive adjective κοµηταί, "long-haired people", to refer to the Persians (Hdt 6.19). The bibliography about the physical and moral representation of Persians as barbarians in Aeschylus' Persians is substantial. For recent synthesis with bibliography, see Hall (1989), Georges (1994) and Mauduit (2007). 67 The epitaph is considered by Athenaeus (Ath. 14.23, 627d) and Pausanias (Paus. 1.14.5) as written by Aeschylus himself: an imitation of his style would then be expected. For parody of the compound words in Aristophanes see e.g. Frogs, 841-842 and 845, which are the first verses pronounced by Aeschylus on stage. 68 Ar. Ran. 1026-1027. 69 Vita 15. 70 φασὶ δὲ ὅτι καὶ τῷ μνήματι αὐτοῦ σειρῆνα ἐπέστησαν, οἱ δὲ κηληδόνα χαλκῆν (Vita 15). "Some say that they put up a statue of a siren on the monument; other, a bronze Celedon" transl. Lefkowitz (2012) modified. On the meaning of the word kèlèdon, "enchantress", which is a suggestion of Huschke for a corrupt manuscript, see Kimmel-Clauzet (2013), 448 n. 99. 71 Collignon (1911 affirming that he "won first prize with his tragic art". 74 Another epitaph is mentioned by Valerius Maximus: it apparently included a reference to Sophocles' last play, Oedipus at Colonus, considered a masterpiece superior to all other tragedies. 75 Hence, there is no other way of commemorating the poet within his tomb than praising his art: the main impression given by all the testimonies concerning Sophocles' funeral, tomb and epitaph is one of perfection and alluring sweetness. 76 Euripides' case is particular, since the poet enjoyed two monuments: a tomb in Macedonia, where he died, and a cenotaph in Athens. The traditions surrounding these two monuments are deeply influenced by the rivalry between Athens and Macedonia, and the political aspects seem at first sight to prevail over the poetical ones. 77 But each monument does allude to specific features of Euripidean tragedy.

Two marvellous stories are told about Euripides' tomb in Macedonia. First, the tomb was struck by lightning. 78 Secondly, two rivers were flowing near his tomb: one was beneficial whereas the other was harmful. 79 These two stories have long since been considered as containing patterns that belong to heroic myth, but it has not been emphasized enough that they both point to the figure of Orpheus. We find the same patterns in Pausanias, who unites the stories where Orpheus is supposed to have been struck by lightning and where his death and tomb are linked to several wonders involving rivers. 80 In fact, Orpheus is so to speak superimposed on Euripides' biographical tradition, which portrays the Macedonian Euripides as a new Orpheus. 81 What does it imply concerning the reception of his work? Without any doubt, the connection between Euripides and Orpheus relies on Euripides' supposed subversion of traditional religion, as presented in the first place by Aristophanes. 82 In Athens, Euripides is supposed to have been mourned by Sophocles and his actors in the odeon, during the proagôn. 83 As for Aeschylus, his status as tragic poet impacts the very proceedings of his commemoration. Euripides also enjoys a cenotaph near the street that leads to Piraeus. No ancient text records the shape of the monument, but its inscription is often quoted. The epitaph refers to poetry in a very conventional way (πλεῖστα δὲ Μούσαις τέρψας), which does not seem specific either to tragedy or to Euripidean tragedy. 84 But the main characterization of Euripides' particular feature may be less in the content of the epitaph per se than in the cultural context of this epigram. Indeed, the epigram is most often credited to Thucydides, and its beginning (Μνᾶμα μὲν Ἑλλὰς ἅπασ' Εὐριπίδου) rewrites the famous sentence of Pericles' funeral oration of the dead soldiers in the second book of Thucydides: Ἀνδρῶν γὰρ ἐπιφανῶν πᾶσα γῆ τάφος. 85 The intertextual echo strikingly stresses 74 κρύπτω τῷδε τάφῳ Σοφοκλῆ πρωτεῖα λαβόντα // τῇ τραγικῇ τέχνῃ, σχῆμα τὸ σεμνότατον. "In this tomb I hide Sophocles who won first prize with his tragic art, a most holy figure." 75 Val.Max. 8.7 ext. 12. 76 In addition to the texts already mentioned, see Plin. Nat. 7.29 (109) and Solin 1.118, where Liber Pater calls Sophocles "the prince of tragic theatre" (tragici cothurni principem) or "his beloved poet" (delicias suas). 77 See Hanink (2008), Kimmel-Clauzet (2013), 91-95, 154-160 and 171-173. 78 App.Anth. 7.48;7.49;Plut. Mor. 59c, Vita IA, 10. The Vita states that both Euripides' monuments were struck by lightning, which seems to illustrate the rivalry between them. 79 Vitr. 8.3.16;Plin. Nat. 31.19 (28). 80 Paus. 9.30. 81 Kimmel-Clauzet (2013), 90-91. 82 E.g. Ar. Thesm. 450-451. Testimonies about Euripides' supposed impiety in Kannicht (2004), 123-124. This is also the vision of the poet given by his death-stories, see [START_REF] Kimmel-Clauzet | Morts, tombeaux et cultes des poètes grecs, Bordeaux: Ausonius éditions Kimmel-Clauzet, F[END_REF]), 88-91. 83 Thom.Mag., Vita, l. 36-38 Kannicht (2004). 84 πλεῖστα δὲ Μούσαις // τέρψας, ἐκ πολλῶν καὶ τὸν ἔπαινον ἔχει. "Having brought great pleasure with his poetry he also won many men's praise." 85 "All earth is the grave of the famous men", 2.43.3. a recurring feature of Euripidean tragedy, namely the lamentation about war dead, which echoes back the human losses during the Peloponnesian War.

There might also have been another way of referring to Euripides' status as tragic poet, if we accept the attractive hypothesis of Andreas Scholl, that the well-known neo-Attic relief from the Istanbul national Museum representing Euripides sitting between Dionysus and the Skènè was placed on his cenotaph: 86 Euripides (represented after the Farnese type) is portrayed sitting to the left, facing the allegory of the Scene, holding a papyrus and a mask of Herakles; behind him stands another mask and a statue of Dionysus holding a cantharus. Such a suggestion remains unprovable for the moment, but its value is to raise the question of the complementary function of an epitaph and an image, since the transmitted inscription and the relief give very different images of the poet. Andreas Scholl studies in the same article another funerary relief that is relevant to our concerns here: the Lyme Park relief, which had previously been attributed to Aristophanes' tomb, and for which he proposes another identification: the poet of the Middle Comic poet Epigenes. The poet is portrayed sitting to the left, holding a papyrus and a comic mask (another comic mask hangs behind him). What seems important here is not the identification of the poet on the relief, but the kind of representation. The relief is dated to the second half of the 4 th century BC (around 340). Whoever is portrayed on it is depicted as a comic poet by the use of "attributes" and peculiar features: the presence of comic masks and a papyrus roll, and the pose, seating (and not standing as actors and musicians, i.e. performers). 87 We can be sure, then, that at that time the tombs can use conventional representations to portray a poet, referring specifically to the poetic genre practiced by the dead. The evolution of dead poets' representations in the literary testimonies surrounding their tombs is undoubtedly corollary to such an evolution in the material culture.

The three canonical poets of tragedy are thus commemorated as poets with common patterns but different details. Not only the design and inscriptions of the monuments, but also funerary customs, are appropriate to them as tragic poets. Nevertheless, each poet is recognized for his own kind of tragic poetry. Aeschylus appears to represent the heroic, perhaps archaic or "epic," kind of tragedy. 88 Sophocles incarnates the perfection of the genre, including its musicality. Euripides is represented differently in Macedonia and Athens, and the location of the tomb undoubtedly played a crucial role in the representation of the dead poet. 89 It seems that the location impacts not only the image of the person, but also, the selection of memorable aspects of his work. Whereas in Macedonia, Euripides' disturbing attitude toward traditional religion is significant, in Athens, no such implication arises. It could even be the contrary if the Istanbul relief, which is has a religious atmosphere, is proven to belong to the cenotaph.

In conclusion, it appears that poetic genres as practiced had a growing influence on the images of dead Archaic and Classical poets preserved by both literary testimonies about his tomb and material culture, that is, by the society as a whole, and not only scholars. The more recent the poet and/or the ancient sources are, the more perceptible this is. If the idea of epic as a genre impacted only marginally the traditions about Homer and Hesiod, if the notion of iambic poetry seems originally absent from the commemoration of the poet, the lyric and tragic poets have early been approached only as poets, and often as poets of a particular kind of poetry. This phenomenon is even more noticeable for Hellenistic poets: Apollonius of 86 Scholl (1995), 236, n. 109. 87 On this typical representation of poets on coins, statues and else, particularly in Hellenistic art, see Schefold (1997). 88 For such a representation in Aristophanes too see Frogs, 1013-1017. 89 Kimmel-Clauzet (2012), 556-570.

  Στησίχορος: ἐκλήθη δὲ Στησίχορος, ὅτι πρῶτος κιθαρῳδίᾳ χορὸν ἔστησεν, "He was called Stesichorus because he was the first to establish (stesai) a chorus of singers to the cithara". Σιμωνίδης: ἔοικε δὲ καὶ Καλλίμαχος τούτοις ὁμολογεῖν. οἰκτίζεται γοῦν τὸ ἄθεσμον ἔργον, καὶ λέγοντά γε αὐτὸν ὁ Κυρηναῖος πεποίηκε τὸν γλυκὺν ποιητήν… "Callimachus seems to agree with this. Certainly he pities the sacrilegious deed; at any rate the Cyrenaic poet has represented him, the sweet poet, saying…" (transl. R. Dyer, Suda on line). 45 οὐκοῦν ὅδε ὁ Φοῖνιξ διαλύει τὸν τάφον τοῦ Σιμωνίδου μάλα ἀκηδῶς τε καὶ ἀνοίκτως, καὶ ἐκ τῶν λίθων τῶνδε ἀνίστησι πύργον: καὶ κατὰ τοῦτον ἑάλω ἡ πόλις, "This Phoenix tore down the tomb of Simonides without care for the burial and pitilessly, and from these stones set up a tower. Thence the city was captured." (ibid.) 46 Οὐδ' ἄν τοι Καμάρινα τόσον κακὸν ὁκκόσον ἀνδρός // κινηθεὶς ὁσίου τύμβος ἐπικρεμάσαι• "Not even

οὐδέ… clause: πύργῳ δ' ἐγκατέλε̣ ξ̣ ε̣ ν ἐμὴν λίθον οὐδὲ τὸ γράμμα ᾐδέσθη τὸ λέγον τόν με Λεωπρέπεος κεῖσθαι̣ Κήϊον ἄνδρα τὸν ἱερόν, ὃς τὰ περισσά ..καὶ] µ̣ νήµην πρῶτος ὃς ἐφρασάμην, οὐδ' ὑμέας, Πολύδευκες, ὑπέτρεσεν, οἵ με μελάθρου μέλλοντος πίπτειν ἐκτὸς ἔθεσθέ κοτε δαιτυμόνων ἄπο μοῦνον, ὅτε Κραννώνιος αἰαῖ 40 Barbantani (2010), 34.

41

Stesichorus as a reincarnation of Homer, App.Anth. 7.75 on which see

Brink (1972)

, 558-560 and Barbantani (2010), 35-39; family (among which two brothers geometrians) linked with Pythagoras: on which see Barbantani (2010), 38-39. I am inclined to think that this is more the result of the location of his tomb than of his poetry. 42 Suda, s.v.

43

The Octagon of Pola had a circular base:

Fischer (1996), 143-158. 44 Call. Aet. fr. 64; Suda, s.v.

  ). 72 Paus. 1.21.1. 73 εἰώθασι δὲ καὶ νῦν ἔτι ποιημάτων καὶ λόγων τὸ ἐπαγωγὸν Σειρῆνι εἰκάζειν (1.21.1; transl. W.H.S. Jones (1917).

Τελευτήσας δ' ἐν τῇ Ἴῳ αὐτοῦ ἐπ' ἀκτῆς ἐτάφη ὑπό τε τῶν συμπλόων καὶ τῶν πολιήτεων, ὅσοι ἐν διαλογῇ ἐγεγένηντο αὐτῷ. "Having died, he was buried on Ios, there on the shore, by his fellow sailors and

Paus. 9.31.4.

Compare with the poems of Alcaeus of Messeny (App.Anth. 7.1 and 7.55), where the burials of Homer and Hesiod are totally reimagined to fit a specific reading of their poetry(Kimmel-Clauzet (2013, 39-40; 50-51; 182).

Cingano (2009), 96-97.

Rotstein (2010), 281-352.

CEG 2, 674: "Archilochos of Paros, son of Telesikles, lies here buried. Dokimos, son of Neokreon, established this as a memorial for him" transl.[START_REF] Clay | Archilochos Heros, The Cult of Poets in the Greek Polis[END_REF].

On this reconstruction, seeKimmel-Clauzet (2013), 141-145.

[START_REF] Ohnesorg | Der Dorische Prostylos des Archilocheion auf Paros[END_REF] (2008). On the Archilocheion and these inscriptions, see[START_REF] Clay | Archilochos Heros, The Cult of Poets in the Greek Polis[END_REF],[START_REF] Ornaghi | La lira, la vacca e le donne insolenti: contesti di ricezione e promozione della figura e della poesia di Archiloco dall'arcaismo all'ellenismo[END_REF] andKimmel-Clauzet (2013), 223-229 (testimonia: 340-352), with further bibliography.

Rotstein (2010), 293-298. The same idea of Mnesiepes' inscription as being 'apologetic' in terms of poetic genre, responding to literary criticism, is developed inOrnaghi (2009), 176-179.

On the use of Archilochus' quotations to support the public memory of the glorious history of Paros in Sosthenes' inscription, seeChaniotis (1988), 67-68 and Kimmel-Clauzet (2013), 228.

Vita β l. 12-13.

Mela 1.13.71.

Rhodes is supposed to have been buried near his mentor, Callimachus, 90 and stones thrown on Aratus' tomb were said to go to pieces, a phenomenon hinting at the poet's Phenomena. 91 Since scholarship about poetic genres cannot be found before the 5 th century BC, it is possible that the early-Archaic poets' biographies and monuments have been concerned with the phenomenon only in a later stage of their development. The definition of their poetic skills could then alter the traditions or only rely on a different reading of them. But the conception of the poetic genres composed did not result in a single image for all poets illustrating the same genre; each kept his special features. The idea of a few canonical authors may have itself modified the representation of each poet: every poet shall give his own contribution to the genre, which justify his selection in the canon.