WFS: A Technical Overview 201 Loudoun Street SW Leesburg, VA A technology development and professional services company Jeff Ehman, Ph.D.

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 2 Topics WFS Overview –WFS Defined –Need and Purpose WFS Technical Details –OGC Service Model –OGC WFS Interface – requests and responses –OGC Filter Specification –Live Examples Compliant Software Resources

Copyright © 2009 Image Matters LLC. All rights reserved. | 3 WFS is an acronym for the Web Feature Service standard WFS is a type of standard known as an interface specification which defines protocols whereby a machine in one location can communicate with a machine in another location regardless of operating system, software vendor, etc. WFS enables requests and transfers of feature geometries (e.g., X,Y coordinate pairs that comprise points, lines, and polygons) and associated topologies. The feature data is encoded in a type of XML called Geometry Markup Language, or GML. The WFS spec was developed through the Open Geospatial Consortium, Inc. ® (OGC) Another OGC standard, Web Map Service (WMS), enables communication for transferring pictures of features, not the feature geometries themselves. What is a WFS ?

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 4 WMS vs. WFS Both are OGC Interface Specifications WMS = Web Map Service; delivers pictures of features from geographic datasets WMS payload is an image (.gif,.tif,.jpeg,.png) WFS = Web Feature Service; delivers coordinate pair and attribute value for the features of the geographic data set. WFS payload is XML; features are expressed in GML

Copyright © 2009 Image Matters LLC. All rights reserved. | 5 An enabling technology for Geospatial Data Roll-up (GDR) Provide access to local data by IDHS Improve coordination for state response Could provide access to others, e.g., for mutual aid –save lives –protect property Improve efficiencies –conserve resources, by moving to automated, on-demand data sharing, and moving away from costly ETL processes Why do we need WFS locally? From DHS GMO – GEA “Geospatial Technology Patterns ”

Copyright © 2009 Image Matters LLC. All rights reserved. | 6 The Problem IDHS County B County C County D County A Most existing internet map and data servers are not “interoperable” –each has vendor-specific access method –access often requires human operator –different data models used; no standard application schemas

Copyright © 2009 Image Matters LLC. All rights reserved. | 7 The Solution IDHS County B County C County D County A Standard framework data models to ensure logical consistency and semantic interoperability Standardized protocols for requesting geospatial information and services via HTTP

Copyright © 2009 Image Matters LLC. All rights reserved. | 8 Interoperability defined Interoperability – the capability to communicate, execute programs, or transfer data among various functional units in a manner that requires the user to have little or no knowledge of the unique characteristics of those units. OGC ® Glossary of Terms -

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 9 ISO General Feature Model : Geographic Features The starting point for modeling of geographic information is the geographic feature. A feature is an abstraction of a real world phenomenon. A geographic feature is a feature associated with a location relative to the Earth. A digital representation of the real world can be thought of as a set of features.

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 10 Characteristics of a Geospatial Feature One Feature per real-world entity Features have a unique, persistent ID Features are typed (tagged with semantics) Features have descriptions (no uniqueness constraint) One or more attributes with name, type value and optional description Variety of attribute data types (integer, real, geometry, raster, feature references, etc.)

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 11 Introduction to Web Services Before the WWW –Isolated, Single-computational-tier Batch processing, hard-copy reports Interactive Applications and Transaction Processing CODASYL and RDBMS Databases –Client (application) / Server (database) –Distributed, Fine-Grained, Multi-tier Processing in controlled (COM, EJB, CORBA) networked processing environments Via the WWW –Information Distribution via Hyperlinked Pages –Interactive (DNS, HTTP, HTML) Web Applications for Human Users –Portals for Centralized, Branded, Access to Pages and Apps –Coarse-Grained Web Services for Software Application “Users” on open standardized (HTTP, XML, UDDI, WSDL, SOAP) WWW –Web Services combined in Service Oriented Architectures

Copyright © 2009 Image Matters LLC. All rights reserved. | 12 service - performance of work (a function) by one for another. There are three related ideas: o The capability to perform work for another o The specification of the work offered for another o The offer [or request] to perform work for another Note the distinction is made between a capability and the ability to bring that capability to bear service - A collection of operations, accessible through an interface, that allows a user to evoke a behavior of value to the user. [ISO – 19119] In a web service, the specification, offering, discovery, request, and performance of work relies upon an Internet protocol backbone Definitions: (web) service

Copyright © 2009 Image Matters LLC. All rights reserved. | 13 OGC General Service Model Registry/ Catalog/ Directory/ Broker ServiceClient Publish Find Bind and Interact Bind Find Publish

Copyright © 2009 Image Matters LLC. All rights reserved. | 14 User Applications Metadata update Metadata search and retrieval Catalog Catalogs Middleware Clients Servers Geoprocessing Services Access to transformed data Service Chaining Direct data access Features Content Repositories Coverages Other data “The Interoperability Stack”

Copyright © 2009 Image Matters LLC. All rights reserved. | Geospatial Web Services Architecture Functional Model Copyright © OGC 2008

Copyright © 2009 Image Matters LLC. All rights reserved. | 16 WFS is a Web Service The WFS specification is a OGC Implementations Specification –WFS, Version 1.1.0, OGC Document –Filter, Version 1.1.0, OGC Document –WFS Schema Corrigendum, OGC Document r1 The WFS operations support INSERT, UPDATE, DELETE, QUERY and DISCOVERY operations on vector geographic features using HTTP as the distributed computing platform. QUERY and DISCOVERY operations are mandatory. Basic interface, as does WMS, allows user/client to specify Bounding Box (AOI) and Coordinate Reference System The OGC FILTER specification defines how to use OGC Query Language to perform query operations (same as Catalog) Returns features as GML encoding What is a WFS ?

Copyright © 2009 Image Matters LLC. All rights reserved. | 17 Purpose of WFS Allows a client to retrieve and update geospatial data encoded in Geography Markup Language (GML) from one or more servers with WFS interface. Web clients and services can combine, use and manage geodata -- the feature information behind a map image -- from different sources. Defines interfaces for data access and manipulation operations on geographic features using HTTP as the distributed computing platform. Uses the OGC Filter grammar, an XML-encoding of a system-neutral query predicate. Developers can build clients that keep complexity “under the hood”.

Copyright © 2009 Image Matters LLC. All rights reserved. | 18 Web Feature Server Specification A Basic Web Feature Server can handle 3 types of operations: –GetCapabilities. Describes using an XML-encoding the capabilities of the service, e.g. the features that are available and the supported transactional operations. –DescribeFeatureType. Provides a description of the structure of a one, many, or all feature types (i.e. the schema that describes the attributes); –GetFeature. Provides access to features based on a filter that constrains the request using spatial and non-spatial parameters. Transactional WFS (“WFS-T”) implementations support these: –Transaction. Insert/Update/Delete features –LockFeature: Lock Feature records for exclusive access. –GetFeatureWithLock: equivalent to GetFeature but locks feature records too Additional (optional) operations: –GetGmlObject. Allows retrieval of features and elements by ID; responds with an XML document fragment containing the result set. The value of the gml:id attribute on the object is used as a unique key to retrieve complex elements.

Copyright © 2009 Image Matters LLC. All rights reserved. | 19 © 2007 Open Geospatial Consortium WFS Interactions WFS stateless HTTP request- response protocol Client WFS document request document request

Copyright © 2009 Image Matters LLC. All rights reserved. | HTTP as a Distributed Computing Platform OGC has defined a suite of Web Service interfaces that have explicit bindings for HTTP. Two primary types of HTTP bindings for invoking operations of a service HTTP GET HTTP POST (also, “Document Literal” style HTTP-SOAP) => the Online Resource for each operation supported by a service instance is an HTTP Uniform Resource Locator (URL). Only the parameters comprising the service request itself are mandated by OGC Web Service Specifications for HTTP.

Copyright © 2009 Image Matters LLC. All rights reserved. | HTTP GET using KVPs HTTP GET – uses keyword-value pairs (KVP), separated by an ampersand “&”, to encode the various parameters of the request, e.g.: befeaturetype&SERVICE=WFS&VERSION=1.0.0&TYPENAME=t opp:wpl_uscitiesover100k Keywords:Values: REQUESTdescribefeaturetype SERVICEWFS VERSION1.0.0 TYPENAMEtopp:wpl_uscitiesover100k

Copyright © 2009 Image Matters LLC. All rights reserved. | HTTP POST using XML HTTP POST – uses XML as the encoding language, e.g.: <DescribeFeatureType Version="1.1.0" Service="WFS" xmlns=" xmlns:topp=" xmlns:tiger=" xmlns:xsi=" xsi:schemaLocation=" topp:wpl_uscitiesover100k This XML would be “POST”ed to

Copyright © 2009 Image Matters LLC. All rights reserved. | 23 "GetCapabilities" Operation Allows WFS to describe itself by its… –feature types offered and their metadata –GML object types supported –spatial reference system(s) supported –geographic area(s) covered –output format(s) (e.g., GML, BGML, Shapefile,etc) –Filter capabilities Server says what it has and does; Client can pick & choose, accept or reject Response: XML document (see also “OWS Common”)

Copyright © 2009 Image Matters LLC. All rights reserved. | 24 How does Client use Capabilities? Client can directly issue GetCapabilities request to particular server Catalog can poll (harvest) Capabilities from servers to build up a “cache” of feature-server descriptions Clients can query Catalog to find data and servers Request syntax: SERVICE=WFS&VERSION=1.1.0&REQUEST=Get Capabilities Response: XML-structured metadata

Copyright © 2009 Image Matters LLC. All rights reserved. | 25 GetCapabilities Request and Response REQUEST=getcapabilities&SERVICE=WFS

Copyright © 2009 Image Matters LLC. All rights reserved. | 26 “DescribeFeatureType" Operation Function: generate a schema description of feature types served by the WFS implementation – the “GML Application Schema” – the structure of the way the feature-level data is available Describes how feature instances are to be encoded: –for input (for transaction operations i.e., Insert and Update) –for output (in response to GetFeature and GetGMLObject requests) Output format is, by default: text/xml;subtype=gml/ EST=describefeaturetype&SERVICE=WFS&VERSION=1. 1.0&TYPENAME=gubs:GovernmentalUnitCE

Copyright © 2009 Image Matters LLC. All rights reserved. | 27 KVP DescribeFeatureType annotated pe&TYPENAME=type_list&OUTPUTFORMAT=text/xml URL (onlineResource) VERSION=m.n.o&Version number REQUEST=DescribeFeatureType&Indicates this operation TYPENAME=type_list&One or more feature type names OUTPUTFORMAT=text/xml;&text/gml;subtype=gml/3.1.1 Note: Bold parameters are mandatory. Note: these parameters apply only for KVP-encoded requests; HTTP POST binding requires a valid XML- encoded request

Copyright © 2009 Image Matters LLC. All rights reserved. | 28 DescribeFeatureType Response RSION=1.1.0&TYPENAME=gubs:GovernmentalUnitCE [Partial Response]

Copyright © 2009 Image Matters LLC. All rights reserved. | 29 "GetFeature" Operation Allows retrieval of features encoded in GML –Must know the information model (Application Schema) of the target features (types, semantics, structure) –Feature Types are listed in Capabilities document –Often, but not necessarilly, the name of the feature element indicates its Feature Type GetFeature contains one or more elements –Queries are expressed using the OGC Filter grammar Responds with one of: –a complete response document (a wfs:FeatureCollection element) –the number of features that a request would return –exception report

Copyright © 2009 Image Matters LLC. All rights reserved. | 30 KVP GetFeature Annotated URL (onlineResource) VERSION=m.n.o&Version number REQUEST=GetFeature&Indicates this operation TYPENAME=type_list&One or more type names FILTER=ogc_filter&Desired background color BBOX=xmin,ymin,xmax,ymax&Bounding box (in lieu of FILTER) OUTPUTFORMAT=text/xml;&text/gml;subtype=gml/3.1.1 RESULTTYPE=results|hits&Full response or count SRSNAME=crs_id&URN encoded CRS identifier Note: Bold parameters are mandatory. Note: these parameters apply only for KVP-encoded requests; HTTP POST binding requires valid XML-encoded request

Copyright © 2009 Image Matters LLC. All rights reserved. | 31 GetFeature XML HTTP-POST Request <GetFeature xmlns=" xmlns:gml=" xmlns:ogc=" xmlns:xlink=" xmlns:xsi=" instance" xsi:schemaLocation=" version="1.0.0" service="WFS" outputFormat="x- application/gml:3:0"> topp:geom , ,61.218

Copyright © 2009 Image Matters LLC. All rights reserved. | 32 GetFeature Response , , Birmingham ,

Copyright © 2009 Image Matters LLC. All rights reserved. | 33 GetFeature Request & Response uest=GetFeature&VERSION=1.1.0&BBOX=-88.15,37.65, ,41.88&TYPENAME=gubs:GovernmentalUnitST , , 37.65

Copyright © 2009 Image Matters LLC. All rights reserved. | 34 OGC Filter logicalOps (AND, OR, NOT) comparisonOps –PropertyIsEqualTo (binary) –PropertyIsNotEqualTo (binary) –PropertyIsLessThan (binary) –PropertyIsGreaterThan (binary) –PropertyIsLessThanOrEqualsTo (binary) –PropertyIsGreaterThanOrEqualsTo (binary) –PropertyIsLike –PropertyIsNull –PropertyIsBetween spatialOps –Equals (property+geometry|envelope) –Disjoint (property+geometry|envelope) –Touches (property+geometry|envelope) –Within (property+geometry|envelope) –Overlaps (property+geometry|envelope) –Crosses (property+geometry|envelope) –Intersects (property+geometry|envelope) –Contains (property+geometry|envelope) –DWithin (property+geometry+distance) –Beyond (property+geometry+distance) –BBOX (property+envelope) Used to constrain the property values of an object type in order to subset (filter) collections of objects Filtering a query is a restriction in order to return exactly the desired subset. There are two main types of filter operators: –Spatial –Comparison. Logical operators are used to combine the other filters to make more complex queries. Filter makes WFS powerful*

Copyright © 2009 Image Matters LLC. All rights reserved. | 35 WFS Software & OGC Compliance OGC offers free tests and testing software for technology providers to confirm that their products are compliant with OpenGIS standards. Providers can then submit products for certification. Certified products can carry the OGC "Certified Compliant" mark to formally signify adherence to OGC standards. For the Web Feature Service implementations, “Certified Compliant” means the software was successfully tested for WFS with Filter Encoding (1.1.0) Products can be registered as “Implementing” – attempted to follow instructions – without complying. List at

Copyright © 2009 Image Matters LLC. All rights reserved. | 36 WFS Server Software – $ **Company has implemented WFS 1.0 or 1.1 for one or more other products not listed here CompanySoftware Name WFS Version OGC Compliant Implementing AutodeskMapGuide Enterprise 2007MapGuide Enterprise 2007, X **CadcorpCadcorp SIS Map Server X CubewerxCubeSERV Web Feature Server (T)X(1.1) ESRI ArcIMS 9.2, 9.3 Server 9.3; GIS Portal Toolkit 2.0 GIS Portal Toolkit X XXXX Galdos Systems, IncCartalinea Geographic Data Server X GenaWareGenaWare 81.0X IntergraphGeoMedia WebMap XX (T) Leica GeosystemsRedSpider Web (T)X1.1 **PB MapInfo CorpMapXtreme X PCI GeomaticsGeomatica - WebServer Suite X Safe SoftwareFME , 1.1X

Copyright © 2009 Image Matters LLC. All rights reserved. | 37 WFS Server Software – Open Source CompanySoftware NameCompliance Status topp.openplans.org GeoServer 1.3 GeoServer 1.5 Compliant 1.0 (T) Implementing lat/londeegree Web Feature Service 2.3Implementing 1.1 UMN MapServer ProjectMapServer 4.2Implementing 1.0

Copyright © 2009 Image Matters LLC. All rights reserved. | 38 WFS implementations (a sample) USGS Framework EPA Superfund: &service=wfs &service=wfs EPA Hazardous Waste: s&service=wfs s&service=wfs EPA Toxic Releases: &service=wfs &service=wfs WRAP TSS: Arkansas GEOSTOR: TURE_LAYERS?version= TURE_LAYERS?version=1.0.0 Galdos Demo: Ionic Boston Demo: Intergraph Demo:

Copyright © 2009 Image Matters LLC. All rights reserved. | 39 WFS Resources OGC: –Specifications WFS V1.1.0 (04-094): WFS Schema Corrigendum (06-027r1): Filter V1.1 (04-095): GML V3.0 (02-023r4): GML V3.1.1 (03-105r1): GML Simple Features Profile V1.0.0 (06-049r1): –Compliance testing: –Resources: Other “recipes”: Lists of implementations – – – – Open Source projects –Deegree: (reference implementation) –Geotools: –Geoserver: –MapServer:

Copyright © 2009 Image Matters LLC. All rights reserved. | Page 40 Image Matters Web Services Activities Open Geospatial Consortium (OGC) Support –Key roles as architects and engineers in development and execution of the Interoperability Program, where OGC specifications are defined, developed, and tested –Co-authors or key contributors to many OGC specifications (GML, SWE, OpenLS, CSW, WCS, et al) –Deep knowledge of OGC specifications, their normative schema and best- practices for application and use. NOAA Support –Developing GML Schemas for IOOS data conforming to OGC O&M and Climate Science Modeling Language (CSML) for use in an OGC SOS Advanced Web Applications, Services & Frameworks –Web 2.0, GeoWeb, Sensor Web, and Semantic Web –USGS, FEMA, EPA, NGA, DHS ICE, DHS S&T, Air Force, Army, others EA Development – Standards-based SOA (S-SOA) –FEA, DHS, USSS

Thanks! Jeff Ehman