Service layer pattern: Difference between revisions

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Revision as of 17:41, 17 August 2010

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{{One source|date=April 2010}}

'''Service Layers''' is a [[Design_pattern_Design pattern (computer_sciencecomputer science)|design pattern]], applied within the [[service-orientation]] [[design paradigm]], which aims to organize the services<ref name='services'>[http://www.whatissoa.com/p11.php services]</ref>, within a service inventory<ref name='serviceinventory'>[http://www.whatissoa.com/p13.php service inventory]</ref>, into a set of logical layers. Services that are categorized into a particular layer share the same type of functionality. This helps to reduce the governance burden related to the service inventory, as the services belonging to the same layer only contain a particular type of solution logic and as a result are easy to maintain.

==Rationale==

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==Usage==

[[Image:Service_Layers_Image_AService Layers Image A.JPG|thumb|alt=Diagram A|Diagram A<br/>In the absence of any layers, services contain a mixture of different types of logic. This makes it difficult to manage these services.]]

[[Image:Service_Layers_Image_BService Layers Image B.JPG|thumb|alt=Diagram B|Diagram B<br/>A service inventory divided into layers where each layer contains the same type of logic.]]

In order to apply this pattern, first it needs to be established which different types of layers are required. This requires creating a service inventory blueprint<ref name='serviceinventoryblueprint'>[http://www.soamethodology.com/p2.php service inventory blueprint]</ref>: a pool of services consisting of candidate services containing candidate functionality. By creating such an inventory, enough information is available to find out the different types of functionality within the intended service inventory. Based on this information, the required types of layers can be established. On the other hand, by applying this pattern at this stage within the service delivery process, the design of the service can be modified so that it contains the relevant type of logic as dictated by the type of the service layer under which this particular service falls.

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Although service grouping can be performed based different types of functionalities, however, to keep the grouping standardized across the enterprise, the actual groups can be based on established service models<ref name='service models'>[http://www.soamethodology.com/p5.php service models]</ref> that depict the most common types of logic that services would normally contain. Depending upon the particular area of the business, a service inventory would usually be divided into task<ref name='task'>[http://www.soamethodology.com/p7.php Task Service]</ref>, entity<ref name='entity'>[http://www.soamethodology.com/p6.php Entity Service]</ref> and utility<ref name='utility'>[http://www.soamethodology.com/p8.php Utility Service]</ref> services. Each of these different types of service models bear specific characteristics that would be eventually demonstrated by the services that belong to the layer, which is based on a particular service model. To design a service based on the aforementioned service models the Process Abstraction<ref name='ProcessAbstraction'>[http://www.soapatterns.org/process_abstraction.php Process Abstraction]</ref>, the [[Entity Abstraction Pattern|Entity Abstraction]] and the [[Utility Abstraction Pattern|Utility Abstraction]] design patterns can be applied as these design patterns help in structuring the solution logic of the services according to specific types<ref name='WK'>Wajid Khattak [http://www.informit.com/articles/article.aspx?p=1583177 Service Layers][Online].Date accessed: 21 April 2010.</ref>.The aforementioned service types are by no means concrete and an SOA could be categorized into a different set of service layers depending upon which characteristics constitute a particular layer, for example, as argued by Bieberstein et al.<ref>Bieberstein. et al.[http://books.google.com/books?id=NISyExeJ5mAC&pg=PA88&dq=%22service+layer%22&lr=&hl=sv#PPA87,M1 Service-oriented Architecture Compass: Business Value, Planning, and Enterprise Roadmap].FT Press, 2005. ISBN 0-13-187002-5, 9780131870024</ref>, an SOA could be divided in to five different layers, namely Enterprise, Process, Service, Component and Object layers.

The application of the Service Layers pattern would necessitate a change in the architecture of the service and the overall architecture of the service inventory<ref name="SvcArch">[[Service-Oriented_Architecture_TypesOriented Architecture Types|SOA Types]]</ref>.

==Considerations==

The application of this design pattern depends upon having enough knowledge about the kind of services in a service inventory before they are actually developed. Consequently, a [[Top-down_and_bottomdown and bottom-up_designup design|top-down]] service delivery approach<ref name="TopDown">[http://www.soamethodology.com/p9.php Top-Down Service Delivery Approach]</ref> needs to be adopted so that a pool of candidate services exists from which the need for different service layers can be established. This will increase the time and efforts required to actually deliver a set of usable services. Secondly, the confidence with which the need for different types of service layers can be established is directly proportional to the size of the service inventory. This means that as more and more services are added to the service inventory, the already established service layers may need to be modified in case new services do not fit into these existing service layers.

== References ==

{{Reflist}}

* Erl et al.,(2009).[http://www.amazon.com/gp/product/0136135161/ref=s9_simi_gw_p14_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-1&pf_rd_r=0FBSA23BKC0AXWVZ5Q9G&pf_rd_t=101&pf_rd_p=51471022&pf_rd_i=507846 SOA Design Patterns]. Prentice Hall. ISBN 0-13-613516-1.

* Mauro. et al. [http://www.computer.org/portal/web/csdl/doi/10.1109/HICSS.2010.336 Service Oriented Device Integration - An Analysis of SOA Design Patterns.] [Online], pp.1-10&nbsp;1–10, 2010 43rd Hawaii International Conference on System Sciences, 2010. Date accessed: 6 April 2010.

* Dave Oliver.[http://geekswithblogs.net/SabotsShell/archive/2006/07/11/84708.aspx SOA Logical Model][Online].Date accessed: 17 April 2010.

* Srikanth Seshadri.[http://www.javaworld.com/javaworld/jw-01-2007/jw-01-soa.html A logical architecture for SOA][Online].Date accessed: 17 April 2010.

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* [http://www.soaglossary.com/ SOA Terms Glossary]

* [http://www.soapatterns.org SOA Design Patterns]

[[Category:Service-oriented (business computing)]]