[preface]

.[big]*OGC Engineering Report*

*COPYRIGHT*

Copyright © 2016 Open Geospatial Consortium.
To obtain additional rights of use, visit http://www.opengeospatial.org/

*WARNING*

This document is not an OGC Standard. This document is an OGC Public Engineering Report created as a deliverable in an OGC Interoperability Initiative and is not an official position of the OGC membership. It is distributed for review and comment. It is subject to change without notice and may not be referred to as an OGC Standard. Further, any OGC Engineering Report should not be referenced as required or mandatory technology in procurements. However, the discussions in this document could very well lead to the definition of an OGC Standard. 

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.[big]*Abstract*

For many years OGC has been developing a suite of standards defining web
services interfaces and encodings for geospatial processing.  The suite
includes a Web Map Service (WMS), a Web Map Tiling Service (WMTS), a Web
Feature Service (WFS), a Web Coverage Service (WCS), a Web Catalogue
Service (CSW), the Sensor Web (SWE) suite of services, etc.  These service
interfaces and their implementations have, more or less, been developed
independently of one another resulting in isolation and poor integration
between them.  For example, consider a map generated by a WMS. A client or
user cannot easily determine which source data was used to create the map
and how to download that source data though an OGC data service such as
WFS or WCS.  Furthermore when one considers the Publish-Find-Bind paradigm,
OGC can only partially support the full potential of this paradigm.  This is
because OGC structured catalogues can only register services in isolation
of other related services and cannot automatically determine the relationships
among services and the resources they offer.

In order to achieve better integration between OGC web services and enhance the
publish-find-bind paradigm, this OGC Engineering Report defines and discusses
three key elements.  These are:

. Defining a new service, called the Web Integration Service (WIS), which allows for the discovery and access to integrated sets of OGC web services deployed at an endpoint.
. Specifying a means of discovering and describing associations between web resources (both OGC and non-OGC). 
. Defining extensions to the OGC catalogue to allow the service to harvest and make discoverable a rich set of linked OGC and non-OGC resources. 

The Web Integration Service (WIS) is an aggregation service whose only purpose
is to provide a list of references to a suite of other, perhaps related OGC services available at an endpoint.

A new operation, named GetAssociations, is defined an an extension such that
existing OGC services (WMS, WFS, WCS, etc.) may implement this operation in
order to support rich auto-discovery.  This operation enables OGC web services
to externalize their internal association knowledge about their content and
relationships to other OGC and external resources.  For example, a WMS would
know if the source data for a layer it offers is a Shapefile, or a WFS feature
type, or another WMS layer (i.e. cascading), or if a WMTS layer exists that
renders the same information more efficiently. This "internal knowledge" can
now be externalized via the GetAssociations operation.

Currently, OGC Catalogues Service instances can harvest the capabilities
document of an OGC web service, register that service, register the existence
of the individual offerings that the service offers and also register the
association between the service and the content it offers.  Thus, the entire
harvesting process is focused on a single OGC web service and consequently
offers a limited scope of discovery.  In order to support rich discovery, a
catalogue needs to be able to automatically register services found at an
endpoint as well as register all known associations among those services,
their offerings and other OGC and non-OGC resources.  This involves harvesting
a service’s capabilities document to determine what content the service offers
but it also involves further interrogating the service to determine of what
(if any) other associations it is aware.  Populated with this enhanced knowledge
a client may now use a catalogue to, for example, find the description of
feature data and then be able to find the WFS that offer that data, a WMS that
renders those features into a map, a WMTS that has a tiled representation of
that data, etc.  In order to support this kind of rich discovery, a new
CSW-ebRIM package is specified that defines ebRIM object types, associations,
classifications and stored queries that support the description of integrated
OGC web service and their artifacts within the catalogue.

.[big]*Business Value*

This OGC Engineering Report is of value because the research and recommended
solution detailed in this document would allow the community to break down the
OGC web service stovepipes that have emerged over the past decade.  With the
existence of the Web Integration Service, the GetAssociations operation and
the extensions to the  OGC CSW-ebRIM Catalogue, the entire publish-bind-find
cycle is significantly enhanced because:

* Publishing becomes more automatic as catalogues can now access the web integration service to determine which OGC web services are deployed at an endpoint

* Finding (i.e. Discovery) is significantly enhanced because OGC web services now advertise all the associations they are aware of allowing catalogues to harvest this information and thus provide much richer discovery capabilities

.[big]*What does this ER mean for the Working Group and OGC in general*

The primary subject of this Engineering Report is to define methods and 
apparatus, via the Web Integration Service, to better integrate a loosely
coupled set of OGC services.  Such a proposal and related discussion is 
within the purview of the OGC Architecture DWG because the overarching
nature of the work presented in the Engineering Report (ER) is germane
to multiple OGC(r) standards.

This ER defines a generic discovery operation named GetAssociations.  The
function of this operation is to allow services to make accessible their
internal knowledge of associated OGC and non-OGC resources resulting in a
richer set of metadata describing each service.  For maximum effect, this
operation needs to be defined for all OGC web services and thus the content
of this engineering report needs to be reviewed by the OWS Common 1.2 SWG for
inclusion into the next version of that standard.

Finally, this engineering report defines an extension package for CSW-ebRIM
(see OGC 07-110r4).  The function of the package is to instrument a CSW-ebRIM
catalogue with the necessary identifiers, associations and classification
schemes to allow catalogues to harvest and properly register the richer set
of metadata made available via the web integration service and the
GetAssociations operation.  These extensions need to be reviewed and commented
on by the ebRIM AP of CSW SWG.

.[big]*How does this ER relates to the work of the Working Group*

The Architecture DWG considers overarching architectural issues that are
germane to multiple OGC standards, including mechanisms for describing and
invoking services in a heterogeneous distributed network.

The work described in this ER is clearly of an overarching nature relating to multiple standards and describing a mechanism for integrating, associating and discovering multiple OGC web services and other OGC and non-OGC resources.

.[big]*Keywords*
WIS, web integration service, associations, GetAssociations, identifiers, catalogue, rich discovery, loosely couples, stovepipe

.[big]*Proposed OGC Working Group for Review and Approval*

This ER shall be submitted to the Architecture DWG, OWS Common 1.2 SWG, and
the ebRIM AP of CSW SWG for review and comment.
