- Bind: used when a service requestor and a service provider negotiate, as appropriate, so the requestor can access and invoke services of the provider. A service requestor typically
uses service metadata provided by the broker to bind to a service provider. The service requestor can either use a proxy generator to generate the code that can bind to the
service, or can use the service description to manually implement the binding before accessing that service. Figure 4 also shows that services can be chained with various
degrees of transparency to achieve larger tasks required by a service
5.2.5 Multi-platform implementation approach
Ensure discovery, access, dissemination and management of all GEOINT data stores through a web-enabled service-oriented-architecture. [Excerpt from NSG Statement of
Strategic Intent]
A Distributed Computing Platform DCP is the collection of protocols, services and conventions that applications use to invoke remote operations. There have been many
popular DCPs over the years including CORBA, DCOM and DCE. Each of these platforms have their strengths and weaknesses. Web Services must also be viewed as a
DCP. Like the others, the web services model has its’ strengths and weaknesses. There are applications for which web services are not appropriate. We can also expect that,
with the development of new distributed computing technologies, web services will eventually become obsolete. Developers of interoperability standards must be prepared
to deal with this continuous change in DCP implementing technology as well as the simultaneous fielding of multiple DCP implementations. The OGC addresses this
problem by separating the business logic conceptual specification from the DCP specific implementation guidance implementation specification.
In practice, COTS vendors have been able to use this model to develop applications that expose themselves over several DCPs simultaneously. They have also been able to
rapidly add support for new DCPs since no changes to the application logic is required.
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Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.
Figure 5 – Services Interoperability Stack
HTTP as Distributed Computing Platform OGC has defined a suite of Web Service interfaces that have explicit bindings for HTTP.
Specifically, there are two HTTP bindings for invoking operations of a service i.e., Sending a message: GET and POST. Thus 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.
SOAP as an OGC Web Services Enabler SOAP is an XML-based remote procedure call protocol that allows messages to be
exchanged between different services. SOAP is used for the bind operation described above. Development of SOAP bindings for the existing OGC Web Service specifications
is underway.
5.2.6 Multi-tiered architecture
Multi-tier architecture also known as n-tier architecture or sometimes n-tier computing refers to the number of logical levels or layers that the various components of an
application occupy. Typical tiers include components for user presentation GUI, presentation logic, business or application logic, data access, and data storage. Tiers can
be physically located anywhere, including on a single computing platform even in a single monolithic application. In single-platform applications the interaction between
tiers is tightly coupled by the language the application is written in andor the architecture of the host operating system. In net-centric, enterprise, Internet-based and Web-Service
applications logical tiers are distributed physically across networks. In such distributed n-tier architectures interoperability between tiers is much more loosely coupled.
Distributing tiers across several computing platforms presents several interoperability challenges managing interactions from tier to tier. Error handling, data exchange, and
Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.
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