One goal of the Public Geospatial Data Project is to offer, in the future, a repository of reusable public geographic data that can support open source geospatial software projects, both inside and outside the foundation.

One big requirement for a potential Geodata Repository is that there be a well-defined baseline for metadata. This can be seen as a quality assurance effort - data won't be accepted without a certain amount of metadata.

The Federal Geographic Data Committee metadata standard emphasises conformance, but doesn't emphasise exchangeability / reusability. FDGC is standard for "Spatial Data Infrastucture" efforts, but doesn't have much of a "geospatial web" orientation.

There are some properties in addition to FGDC which it would be really useful to have - different distribution channels like WFS, bittorrent which have come into existence since FGDC was originally defined. For many elements, FGDC asks for full-text descriptions. More structure in descriptions would help with automating discovery or re-use.

This is perpetual work in progress. See also:

Draft Metadata model

Attempting to abstract the minimal metadata model below (DClite4G) out into Geodata Metadata Model (see there), which serves for a metadata management tool. This is what OSGeo Geodata Committee participants have identified as their core needs for metadata.

It was generated from an RDF model. This picks an arbitrary namespace for an OWL schema that maps to most, if not all, of the FGDC mandatory properties and provides some extra ones.

Data Set

Title: Title of the data set. Corresponds to Dublin Core title
Description: Text description of the data set. Corresponds to Dublin Core description element.
Originator
- Person: A person responsible for publication of the data set - name and contact email address. These properties are well-defined in the FOAF vocabulary.
- Organization: A organization responsible for publication of the data set - name and contact email address. These properties are well-defined in the FOAF vocabulary.
Spatial Data Organization: Vector, Raster or Point data, as described in FGDC. (cf http://biology.usgs.gov/fgdc.metadata/version2/sdorg.htm )
Datasource: URL from which the data can be downloaded via different protocols
- WFS: For Vector data in GML
- File at HTTP URL: For Raster data described in GML
- BitTorrent: URL of bittorrent .torrent tracker file.
- Other Web API: For example, OpenStreetmap API ( http://wiki.openstreetmap.org/index.php/REST )
License information: Emphasis on public geographic data licenses: PGL, possible LPGL, Public Domain, Creative Commons-type licenses. These can be represented by URLs.
Publication date: Corresponds to Dublin Core date: ISO compliant date of publication.
Timespan
Time Period
- start date and end date
- single date
- Extents
Spatial Domain: A lot of this can be inferred either using GDAL/OGR or collected from a WMS/WFS GetCapabilities. It would be nice to bypass human error on collecting this kind of metadata.
- bounding coordinates: FGDC specifies north, east, west, south bounding co-ordinates. It doesn't specify a projection in which these should be described. For reasons of simplicity it could make sense to require these be in WGS84 (EPSG:4236) - for the same reasons GeoRSS decided to mandate WGS84, rather than complicate matters by dictating that people also specify an SRS.
- Projection (Raster, Vector, Coverage): Original projection of the data (reference to an ?)
- Horizontal and vertical datum;
- Horizontal and vertical units.
- Resolution (Raster,Coverage): (property of DataSet). e.g. map units per pixel where map units are defined by SRS. can be different in horizontal / vertical axes e.g. non square pixels
- Colour Depth (Raster): 8/16/24 bit etc - this is useful rather than required
- Transparency (Raster)
- Scale (Vector):Map scale at which vectors are considered accurate. Quantified as a fractional/dimensionless number - 'inches per inch' - on a scale between 1 and 0 - or inverse scale such as 1:50000 - and we would want to store this in a consistent way.
Layers: DataSet has multiple Layers
- Name
- Description
- Extent: can be non-rectangular
- Scale Hinting: minscale / maxscale - cf resolution and scale - are these actually properties of layers and not really of data sets? (eg data set contains multiple layers - will they be in any way likely to contain different scale properties?)
- Optional extra properties
Taxonomy/Ontology: Currently undecided; would be good to refer this to current well-known thesauri for data themes.

Discovery

Requirements

A discovery resource is essential to expose resultant metadata as per this document. Below are requirements:

Publish:

ability to publish/register a web service
ability to publish/register a static resource
ability to harvest and classify public and private resources
ability to establish and maintain user/group/role based authentication
ability to provide a RESTful authentication mechansim

Find:

ability to discover the existence of a web service
ability to discover the existence of a resource which is available via web services (i.e WMS layer, WFS feature type)
ability to discover the existence of a static resource (dataset, document, etc.)

Bind:

ability to perform discovery operations with spatial, aspatial and temporal predicates
ability to provide a RESTful request API
ability to provide responses in XML
ability to expose resource/service metadata in a manner which facilitates dynamic connection to a resource/service

Webcrawlers perspective or: How to boost your geodata?

Geoinformation content needs to be published and get disseminated somehow before it is being found by users. Following are some thoughts to help discovery/search services/brokers and their webcrawlers/harvesters/aggregators to do a better job. So the main question here is: What can content owners do to promote their information. It's mainly registration, declaration and citation. -- Stefan 11:25, 2 October 2006 (CEST)

Self-registration through content provider (like DNS)
- submit URL or ping (RSS)
- register through UDDI (if SOAP is 'unavoidable')
Self-declaration:
- Machine-readable only ('invisible'):
  - GeoRSS feed of feeds which contain GeoRSS encoded metadata records
  - OPML (if RSS)
  - Something similar to robots.txt
  - HTML link: <link rel="alternate" type="application/rss+xml" title="RSS" href="http://rss.news.yahoo.com/rss/tech">
- Visible/human readable:
  - Feed icons
  - Chicklets
Citation through others:
- XML link or relationship inside metadata record (see also 'friend' in OAI-PMH metadata set header)
- HTML link pointing to Webpage (suboptimal)

Note: See also "RSS auto-discovery": e.g. '"Blog Optimization", SES San Jose (aug. 2006): 1. Submit your feeds... Or: "Pimp My Blog in 8 Steps" (sept. 2006): (...) 3. Sign up for feedburner.com, (...) 8. Enable auto discovery (feed icon, chicklet).'

Information model for metadata exchange

This is the http://tinyurl.com/kfkyv model (:->).

Some design considerations:

This is a minimal metadata information model regarding to a metadata exchange protocol for harvesting (e.g. no filter nor GML implementation needed) and according to the ideas about a Simple Catalog Interface/protocol.
Based on Dublin Core (DC) and Catalogue Services Specification 2.0.1, OGC 04-021r3, p.22.
Dublin Core need refined semantics of some properties/attributes.
Have had hard times with the abundance use of namespaces. This is because DC specs and other XML 'practices' specialize properties/attribute types instead of specializing whole classes.
All properties/attributes have cardinality [0..1] except for identifiers (which are mandatory) and for those attributes which are really needed (as unbounded) for automation!
Take all information one can in an automated manner, e.g. from data set resource.

Details:

Services are included in attribute 'format' in the sense that WMS, etc. are just protocol bindings to geodata. Real well known services on it's own like filter or label placement services have a place there too. They could be still detected by challenging them with GetCatabilites (taken from OWS/WxS).
Indicating of quality of service could be a nice task for search service provider; no need to add it as attribute
Relationships between features is part of schema metadata: How to handle this...?

Dublin Core lite for Geo (DClite4G)

Aligned and rearranged to mode after some discussions on osgeodata-list and geotools-devel-list. Next steps: first consensus on approach/fields, then consensus about which encoding (DC, RDF or GeoRSS?). - Stefan 08:33, 26 September 2006 (CEST)

Figure: Analysis UML class diagram of minimal metadata information model 'Dublin Core lite for Geo' (DClite4G) which consists of a single entity set (green); two entities/instances/records are shown, a 'dataset' (left, grey) and a 'service' (right, red).

Class diagram of 'Dublin Core lite for Geo' (DClite4G)

Dublin Core lite for Geo (DClite4G) (Mandatory subset of DC elements plus georesource relationships, some XML content exept dc:identifier may be null/empty):

Attr. name	Cardinality	Attr. type	Explanation	Poss. to autom.?	Status
dc:identifier	[1]	URI	An unambiguous reference to the resource within a given context. Used for reference in many places in Web space but including als dc:relation subtypes like dct:hasPart. (see also OAI-PMH and GeoTools which speaks of base URLs for services and of 'data access points') (Clarification needed: Each metadata provider can define its context?)	System generated	Ok?
dc:title	[0..1]	string (XML encoded)	A name given to the resource (regardless e.g. of naming restrictions of file systems). If a layer or file name exist in addition to a title this name can be wrapped in square brackets (tbd! proposal) and concatenated at end of this title string.	GetCapabilities	Ok
dct:abstract	[0..1]	URI or string (XML encoded)	A description of the resource. Either a URI reference to a human readable resource or a string. In case of dc:type 'service' (OWS) its the abstract (string) from of GetCapabilities document (GeoTools ServiceInfo has two fields: abstract and description...?) Subtype of dc:description; we use this as WMS, csw:record and ISO 19115 are using it.	GetCapabilities	Ok
dc:type	[0..1]	enumeration	The nature or genre of the content of the resource. 'dataset' or 'service' else 'document, 'text', 'image', 'sound', etc. (see DCMI type (controlled) vocabulary). Could be more specific but the more unlikely to agree here: 'geodata', 'vector', 'raster', 'grid'?) or 'data access service' or 'WPS' (= Web Processing Service; services which have no specific georesource they are responsible for) or documents like OGC:SLD, OGC:WMC etc. (GeoTools distinquishes GeoResourceInfo and ServiceInfo and somehow by querying 'getGeoResource().resolve(GridCoverage.class, null)')	Can be derived; (GetCapabilities)	Ok?
dc:format	[0..1]	URI	A machine readable reference to an xml schema namespace URI, internet media type (recommended) or mime type which contains the either the schema of the information model of the 'original' resource (dc:type 'dataset') or a description of the service (dc:type 'service') as key-value pairs (so that multiple schemas are possible, like in namespaces syntax)	(GetCapabilities)	Ok
dct:spatial	[0..1]	dcmiBox:Box with CRS	Subtype of dc:coverage. (CRS=WGS84; other possible values offered by dct: Point and TGN)	Boundary/BBox from resource; GetCapabilities	Ok
dct:modified	[0..1]	date	Date of last (published) change of resource (see W3C Encoding rules). Subtype of dc:date	Timestamp of resource; GetCapabilities	Ok
dc:subject	[0..1]	string (ASCII)	A keyword list; e.g. ISO 19115 classification list. (clarification needed: separated by comma and/or semicolon?)	GetCapabilities	Ok?
dclite4g:onLineSrc	[0..*]	URI	If type 'service' then this is the baseURL to it (similar to iso19115). If dc:type 'dataset' it's either a dc:identifier which points to a metadata record of type 'service' or a full URI to e.g. ftp:// host.com/path/filename. Subtype of dc:relation; see here. (or use cld:isAccessedVia?)	Can be derived	Ok?
dct:hasPart	[0..*]	URI	A dc:identifier. Only applicable if type 'service'; N/A for type 'dataset'. A dc:identifier which points to a metadata record of dc:type 'dataset' for which it is 'responsible' for. Subtype of dc:relation.	Can be derived	Ok?
dc:source	[0..1]	URI or string (XML encoded)	Description from which the present resource is derived, lineage information. Either an URI reference to a human readable resource or a string. (Note: Server base URLs and file URIs are handled elsewhere)	Up to data owner	Ok

Remaining (optional) DC elements:

Attr. name	Cardinality	Attr. type	Explanation	Poss. to autom.?	Status
dc:publisher	[0..1]	string (XML encoded)	Civic Address: if type service derived from GetCapabilities ('ContactInformation') else flattened KML style (= xAL) (still awaiting consensus in other OGC specs. or GeoRSS)	Up to data owner, GetCapabilities	Ok?
dc:language	[0..1]	enum	RFC 1766 (ISO 639, followed optionally by country ISO 3166)	(could be guessed from title/description?)	Ok?
dc:rights	[0..1]	URI or string (XML encoded)	License information about the resource. Probably also disclaimers. Either a URI reference to a human readable resource or a string. Machine readable license is an issue though: This could be an starting point.	Up to data owner, GetCapabilities	Ok?
dc:relation	[0..*]	URI	A reference to a related resource. These are some useful subtypes. One usage could be a machine readable reference to other metadata providers in order to let discover other (meta) data providers. See also dc:hasPart and iso19115:onLineSrc above. Note that OAI-PMH has such a relationship called 'friends' but on the metadata collection/set level.	Up to data owner	Ok?

Legend: 'Poss. to autom.' means Possible to automate

Remarks:

General:
- DC attributes/properties left as they are...: Audience; Contributor; Creator.
- All attributes/properties have at most cardinality 1 except iso19115:onLineSrc and dct:hasPart (and dc:relation from complementary part of dclite4g).
- Depending on the modeling approach, even these elements can become cardinality 1. NOTE that datasets (geodata resources) and services (data access services) in principle have a many-to-many relationship: Here a geodata resource (dc:type dataset) can have many iso19115:onLineSrc elements and a dc:type data_access_service has only one dc:description which can be a GetCapabilities document.
- No additinal DC attributes/properties required; few them needed to be specialized (see dct:...); ** See for some general explanations about dc/dct here.
- Some attributes/properties still need unambiguous meaning (see tbd.).
- Assume metadata (as opposite to many geodata sets) is always free and open information, like Creative Commons Share Alike
- An encoding still has to be discussed (see following example). need schemaLocation in OSGeo!?
Details:
- Sorted out or highly disputed (non-DC) elements: fees, scalehint, harvestinterval.
- dct:modified and dct:spatial can be sync'ed from dataset.
- Attribute 'relation': This was'nt discussed yet. Simply helps harvesters to discover more (meta) data providers.
- Attribute 'publisher': Carl mentioned such a structure here which includes StreetAddress, addressee, primaryAddressNumber, streetName, city, state, zipCode, countryCode (like in KML and behind Google geocoding service!?)
- Keywords is included in attribute 'dc:subject'; I think people have a hard time to agree on an enumerated list (see the success of folksonomy).
- GetCapabilities adds following attributes (not yet modeled here): Fees, ScaleHint and Style.
Note that OAM-PMH...
- puts a XML envelope around this metadata and adds a header containing two attributes: 'identifier' to identify an metadata record and 'datestamp' as date of last (published) change of metadata record.
- requires to define a name for metadata sets. Let's don't care about this yet.

Examples

Some examples of DClite4G instances/records: (legend: 'literal' is a constant, // is a comment)

A web mapping service instance example derived from GetCapabilities: Mapping OGC:WxS GetCapabilities to a service instance. Can also be called a 'data access point' (Note GetCapabilities finally needs to be delivered by some service owner!):

 dc:identifier      = baseURI of the service
 dc:title           = WxS Service/Title
 dct:abstract       = WxS Service/Abstract
 dc:type            = 'service'
 dc:format          = namespace to OGC:WxS schema.xsd
 dct:spatial        = Root BoundingBox // from Capabilities XML
 dct:modified       = timestamp // e.g. from HTTP header or updateSequence
 dc:subject         = WxS Service/KeywordList
 dclite4g:onLineSrc = baseURI of WxS 
 dct:hasPart        = a dc:identifier // points to each Layer element
 dct:hasPart        = another dc:identifier, etc.
 dc:source          = null // N/A. Note: Not meant as an OnlineResource
 dc:publisher       = WxS Service ContactInformation/Organization
 dc:language        = maybe HTTP header for lang (ISO3166 code)
 dc:rights          = WxS Services Fees/AccessConstraints
 dc:relation        = null // for future use

A dataset example derived from GetCapabilities: Mapping OGC:WxS GetCapabilities to a dataset/georesource/data access point:

 dc:identifier      = a unique data access point?
 dc:title           = WxS Layer/Title
 dct:abstract       = WxS Layer/Abstract
 dc:type            = 'dataset' 
 dc:format          = namespace to format
 dct:spatial        = BoundingBox from Layer/BoundingBox
 dct:modified       = timestamp from HTTP header maybe or updateSequence
 dc:subject         = Layer/KeywordList
 dclite4g:onLineSrc = a baseURI of WxS // a dataset binding
 dclite4g:onLineSrc = another baseURI of WxS // a dataset binding
 dct:hasPart        = null // N/A
 dc:source          = null // Note: Not meant as an OnlineResource
 dc:publisher       = from Service if available?
 dc:language        = from Service if available?
 dc:rights          = from Service if available?
 dc:relation        = from Service if available?

A dataset example delivered by a dataset owner:

 dc:identifier      = a data access point defined by dataset owners context
 dc:title           = entered by dataset owner
 dct:abstract       = entered by dataset owner
 dc:type            = 'dataset' 
 dc:format          = namespace to format entered by dataset owner
 dct:spatial        = BoundingBox from data warehouse
 dct:modified       = file timestamp from data warehouse
 dc:subject         = keyword list entered by dataset owner
 dclite4g:onLineSrc = a http URI entered by dataset owner // dataset binding
 dclite4g:onLineSrc = a baseURI of a WxS entered by dataset owner // another binding
 dct:hasPart        = null // N/A
 dc:source          = entered by dataset owner ? Note: Not OnlineResource
 dc:publisher       = entered by dataset owner
 dc:language        = entered by dataset owner (or derived?)
 dc:rights          = entered by dataset owner
 dc:relation        = null // reserved

A dataset example with XML encoding:

Notes:

Example values are only for explanation purposes and purely fictive.
XML Schema (= geometadc.xsd? or dclite4g.xsd?) still tbd.
This record is not yet validated!
Took 'dclite4g' as envelope name.

 <dclite4g:qualifieddc 
   xmlns:dclite4g="http://www.osgeo.org/schemas/dclite4g/0.01" 
   xmlns:dc="http://purl.org/dc/elements/1.1/" 
   xmlns:dct="http://purl.org/dc/terms/" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
   xsi:schemaLocation="http://www.osgeo.org/schemas/dclite4g/ dclite4g.xsd">

   <dc:identifier>f264-77d2-09ce-aa39-f0f0</dc:identifier>
   <dc:title>National Elevation Mapping Service for Texas</dc:title>
   <dc:description>Elevation data collected for the National Elevation 
    Dataset (NED).</dc:description>
   <dc:type>dataset</dc:type>
   <dc:format>...uri to the schema of the information model (xsd, realxng, schematron, ili, ...)</dc:format>
   <dct:spatial>
     <Box projection="EPSG:4326" name="Geographic">
       <northlimit>34.353</northlimit>
       <eastlimit>-96.223</eastlimit>
       <southlimit>28.229</southlimit>
       <westlimit>-108.44</westlimit>
     </Box>
   </dct:spatial>
   <dct:modified>2004-03-01</dct:modified>
   <dc:subject>Elevation, Hypsography, and Contours</dc:subject>
   <dclite4g:onLineSrc>uri:http://www.osgeo.org/geodata/ned_grid_georss.xml</dclite4g:onLineSrc>
   <dclite4g:onLineSrc>uri:http://www.osgeo.org/services/wms/</dclite4g:onLineSrc>
   <dclite4g:onLineSrc>uri:http://www.osgeo.org/geodata/ned_grid.shp</dclite4g:onLineSrc>
   <dc:source>Lineage: Based on 30m horizontal and 15m vertical accuracy.</dc:source>

   <dc:publisher>U.S. Geological Survey</dc:publisher>
   <dc:language>en</dc:language>
   <dc:rights>uri:http://www.usgs.gov/pubprod/</dc:rights>
   <dc:relation>g264-77d2-09ce-aa39-g0g0</dc:relation>
 </dclite4g:qualifieddc>

Other Relevant Info

Simple_Catalog_Interface
OSGeodata on GISpunkt Wiki - These pages are about the search of an open, lean and mean "protocol for the incremental exchange of metadata about geographic resources between systems". Profiled specifications like WFS or OAI-PMH are currently on our short list. Delving into 'Open Archives Initiative Protocol for Metadata Harvesting' (OAI-PMH) is strongly encouraged. It's a low barrier interoperability specification based around metadata harvesting model, it's stable (subsequent revisions are backwards compatible) and uses unqualified Dublin Core as default metadata information model; there exist open source tools (like OAICat) and it has been adopted among others by Google and Yahoo! but it's not a search protocol.
See here a comparison between CSW, WFS and OAI-PMH.

References

Geospatial

FGDC geospatial metadata model

GEON geospatial metadata model

DIF geospatial metadata model

GeoRSS

WFS

GeoAPI contains an implementation of ISO 19115

RDF

Resource Description Framework

RDF Primer

OWL Web Ontology Language Guide

Semantic Web for Earth and Environmental Terminology OWL Ontologies at NASA

Dublin Core metadata model for documents

FOAF metadata model for people and organisations

DOAP metadata model for open source software projects and code repositories

Notes

metadata isn't an easy task. The balance between completeness and people simply ignoring to generate it...

I wish I had had a prexisting plan of how to index and search for the data sets on extent and 'type' that we were adding

From Geodata Packaging Working Group:

- Specifications of a data set
  - Creator
  - Date
  - License
  - Data Type
  - Topic
  - Spatial Extent
  - Coordinate System/Projection
  - Target Scale/Precision
  - Attribute Data

Comments

I would like to propose an additional element for the metadata model--data source (or lineage). If the data is derived from some other data, we should be able to backtrack and look at its parent/s. "Lineage" is a conditional element in FGDC but I think it's important enough that we should include it in our model. I suppose this can also be included in the Description but wouldn't it be nice to have this included as a required element? This is useful when checking for errors/consistency. -Perry

Geodata Metadata Requirements

Contents