Re: Extension/Extensibility examples in W3C Specifications:

An additional reason (point 2.) might read

- some technologies are explicitly intended as a foundation for 
extensions, e.g. XML, RDF and XHTML

[At least some member of RDF Core, probably all those who were also 
members of WebOnt, see the value of RDF being realised in OWL.]

Another issue which might be worth a short piece of text is if you are 
building an extension, you should consider what happens when you 
intereact with other extensions. Can extensions be combined? I don't 
think WebOnt explored this, and it may have impacted our design 
decisions if we had.
I guess that too could be a further bullet point under 2.
e.g.

- your specification is itself an extension of some other spec. Maybe 
the extensibility mechanism you are using, can continue to be used to 
extend the extension.



Lynne Rosenthal wrote:

> 
> The following is my attempt at summarizing a very interesting and 
> informative discussion on extensions/extensibility and organize it in 
> some way, so that we can incorporate it in the rewrite of the 
> Specification Guidelines (SpecLite).   Please let me know where I've 
> misrepresented something or just got it wrong as well as helping to add 
> more detail and examples.   Additionally, I've indicated questions using 
> @@.
> 
> 1.  Definitions:  There is no clear definition of extension or 
> extensibility, although both terms are used and seem to be understood 
> within the context of their use.  They are tied closely to their (base) 
> specification and vary as to the specificity of their meaning, use, 
> invocation, etc.  However, there are characteristics that apply and a 
> general definition can be derived.
> Extension: characteristics that seem to always be true
>  - additional feature (@@functionality?) to the specification.
>  - does not break/negate the base specification
> @@Are the following always true?
>  - does not redefine existing technology (counterexample: CSS- By 
> providing alternatives to another technology (@@is this true?)
> - non-standardized functionality or capability beyond the scope of the 
> specification. (counterexample: ??)
> 
> Therefore, general definitions:
> a) Extension is the incorporation of additional features, beyond what is 
> defined in the specification.
> 
> b) Extensibility is the ability of a specification to accept extensions 
> in a defined way.  A specification is extensible if it provides a 
> mechanism for any party to create extensions that do not interfere with 
> conformance to the specification.
> 
> 2.  Reasons for designing extensibility into a specification
> - there will be extensions, it is inevitable.
> - to accommodate the changing technology and information on the Web
> - provides a stable, useful, framework to manage the rapid pace of 
> technology change
> - 'test drive' new functionality that may migrate into future 
> specifications
> - provides a consistent manner, leading to predictable handling of 
> extensions
> - less change for extension to interfere with conformance to the 
> specification and a better change for achieving interoperability.
> 
> 3.  Planning for extensibility
> - depends on the specification and the technology.
> - can be included as a provision or feature in the specification 
> (example: XSLT, WSDL, others?)
> - can be based on other specifications (example: CC/PP based on HTTP 
> Ext. Framework, Owl's semantic extensions of RDF)
> - can be a specification only about extensibility of the technology 
> (example: Component Extension (CX) API, HTTP Extension Framework, XHTML 
> Modularization?)
> 
> 4. What is being extended
> - the technology defined by the specification (example: XSLT, WSDL, 
> others?)
> - another technologies (RDF+OWL where OWL adds additional constraints, 
> others?)
> @@Where does XHTML Modularization fit? Where does CSS-3 fit?
> 
> 5.  Different mechanisms.
> Again technology and application dictates the best strategy and mechanism.
> - mechanisms take different forms:
>   -- conformance criteria/rules (XHTML),
>   -- framework (HTTP ext framework, XHTML Mod),
>   -- techniques (XSLT, WSDL)
> @@ is this helpful?  is it correct?  Are there other mechanisms?
> 
> 6.  Additional items
> - error handling  how to handle unknown extensions (@@ does this apply 
> to everything or just agents? )
> - unique identifiers and declarations indicate extensions (HTTP ext 
> framework, CC/PP) (@@ are there are examples of this?)
> 
> Thank you to all who have shared their knowledge, examples, and 
> comments. I welcome all and any additional comments, examples, draft 
> text, etc.
> --Lynne
> 
>

Received on Thursday, 6 May 2004 17:11:26 UTC