Chris Kuruppu

NWS Office of Science and TechnologySystems Engineering Center

(Skjei Telecom)10/6/09

AssumptionsThe SoS approach has been chosen as the best

engineering approach as seen in documents such as:

NextGen Weather Plan – NEWP “Develop a new weather data distribution architecture,

leveraging net-centric standard and existing architectures”

NextGen Air Transportation System Weather CONOPS 4-D Weather Functional Requirements for NextGen Air

Traffic Management JPDO NextGen CONOPS NextGen WIDB – IT Needs

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SoS FundamentalsA System of Systems....

Has operationally independent elements. Component systems are useful in their own right.

Has managerial independent elements. Component systems maintain current operations

independent of the SoS.

Has evolutionary development. A SoS is scalable.

Has emergent behavior The SoS performs functions that do not reside in any

one component system.

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SOA ConceptsService Oriented Architecture (SOA)

represents a model in which logic is decomposed into smaller, distinct units of logic.

These ‘distinct units of logic’ are ‘services’ in an SOA context.

Services are made discoverable by the Registry / Repository by their WSDL Service Description and associated metadata..

Users/Systems discover services (to obtain products/data) by querying the Reg/Rep.

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Web Services BasicsWeb Services is fundamentally comprised of the

following technology/standards.XML – eXtensible Markup Language is a set of rules

for electronically encoding documents.SOAP – Simple Object Access Protocol is a

specification for exchanging structured information.

HTTP – HyperText Transfer Protocol is an application- level protocol (from OSI network stack model).

WSDL – Web Services Description Language is an XML- based language that provides a model for

describing Web services.5

Web Services Basics cont...XMLPopular standard format for the exchange

of data and documents. Underlies SOAP and WSDL.Platform independent.Example Code:

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Web Services Basics cont...SOAPXML-based messaging specification.Known XML format.Utilizes HTTP POST/GET as underlying transport

protocol.

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Web Services Basics cont...HTTPUtilizes request methods to indicate the desired

action to be performed on the resource (URL).HTTP GET request retrieves a resource from a

server.HTTP POST request is used to send data to a

server to be processed in some way.

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Web Services Basics cont...WSDLXML-specification used to describe ‘services’.

Provides description of service interface, and information on where to find the service on the network (URL).

Describes two aspects of a service: Abstract interface and Concrete Implementation.Abstract Interface – describes general service

structure (operations, operation parameters).Concrete Implementation – binds the abstract

interface to a network address, communication protocol, and data structures. i.e. concrete implementation binds the service and invokes its various operations.

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Web Services Basics cont...WSDL

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Web Services Basics cont...Web Services offer a connection technology.

Platform to connect the ‘services’ in an SOA

For example, Web Coverage Service (WCS)..-Has 3 types of requests:

GetCapabilities – Service metadata (XML doc) DescribeCoverage – Full description of one or more

coverage (XML doc) GetCoverage – One coverage (known format)

-Uses HTTP POST/GET to connect to a service (which has an associated URN/URI/URL)

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What are Services?Services encompass logic.

Services can cover a varying amount of logic (ie. business rules, or something much smaller).

Very similar to ‘objects’ in Object Oriented Programming (OOP). SOA is an alternative way of organizing code, based on

services instead of a hierarchy of objects.

Services are autonomous. Services are self-governing/stand-alone.

Services share schemas and contracts, not classes and types.

Services are designed to exchange contracts for behavior and XML schemas for data structure.

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What are Services? continued..Services need to have explicit boundaries.

To maximize code reuse and sustain service longevity.

Services that have overlapping logic can potentially lead to circular dependencies.

Ties to services being ‘loosely-coupled’.

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Services continued..

System 1

Service A

Service B

Service C

Registry /Repository

Services A,B,C

Publish Service Descriptions / Metadata for A,B,C

Query for Data

Return Services needed to get data

Physical Connection Exists

User Invokes Services to get data

User Requested Data

via physical connection

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Registry /Repository

System 1

System 2

System 3

Publish Service Descriptions / Metadata

Publish Service Descriptions / Metadata

Publish Service Descriptions / Metadata

Query for Data

Return Services needed to get data

System 4

User Invokes Services to get Data

User Requested Data

User Requested Data

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How does it all fit together?

An SOA is an approach to a SoS architecture.Legacy systems?

Implementing a service-oriented front end (Edge Servers) for a legacy system will expose that same business logic to an entirely new set of applications/data.

New systems and legacy systems can leverage each other’s functionality through the SOA implemented by Web Services (essentially the SoS).Instead of many point-to-point links, systems are

network-enabled.16

SOA Visual

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...Questions/Discussion?

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