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Re: [ontolog-forum] Legacy systems

To: "Obrst, Leo J." <lobrst@xxxxxxxxx>
Cc: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Barker, Sean (UK)" <Sean.Barker@xxxxxxxxxxxxxx>
Date: Mon, 19 Nov 2007 10:55:12 -0000
Message-id: <E18F7C3C090D5D40A854F1D080A84CA47FE6C9@xxxxxxxxxxxxxxxxxxxxxx>

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contrary non-withstanding. It is the opinion of the author, and does not
represent an official company view.    (01)

 Sean Barker
Bristol, UK    (02)

> Some of us advocate:
> 1) Unbundling/decomposing your existing systems over time 
> into services. This is hard work and will be going on for a LONG time.
> 2) When new systems/applications are considered, design them 
> as services, i.e., reusable discrete (as much as possible) 
> components which can be composed to create new systems/applications. 
> 3) Build services which are described semantically. This 
> description can be initially a purely natural language 
> description (implicit model), or an ontology (explicit 
> model). In either case, you will need grounding in natural 
> language descriptions: that need does not go away with the 
> development of a logical model (you still need to describe in 
> natural language what you mean by the logical expression, so 
> humans can inspect both and gauge conformance of the logical 
> description with the natural language description). 
> 4) For existing (legacy) systems, you need to plan their 
> evolution toward your semantic/SOA paradigm. All systems have 
> a maintenance cycle. Transforming legacy systems to a new 
> paradigm incurs such huge costs that you cannot typically do 
> that. Instead, you must rely on the next bullet: 
> 5) Abstracting functional/procedural calls into the legacy 
> system (assuming you can do so, i.e., if the API is rich 
> enough to support this; if it isn't and you just call the 
> monolithic system and get its final results, this effort will 
> not work). Create wrappers for these calls into the legacy 
> systems. They become rudimentary services. But most legacy 
> systems are not amenable to this, so you must focus on the 
> next bullet:
> 6) For standalone, monolithic legacy systems (which you 
> cannot create functionally distinct calls into), then you 
> must wrap the whole system, i.e., treat the whole system as a 
> single service and try to create a semantic model (ontology) 
> for what that system is doing. The system may or may not use 
> a distinct database.     (03)

May I add    (04)

7) Encapsulate multiple legacy systems, using some form of "active
encapsulation", such that a service request is fulfilled by taking
information/functionality from multiple legacy systems. Here, the active
encapsulation agent has the role of decomposing a service request into
calls to each legacy system and composing the response.    (05)

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