May 29, 2007 5:19 AM
Web 3.0 - Conversion and translation of context and semantics
Context of an object/service is the information about the interactions and circumstances of an object/service. This context can be defined as an interface with operation, messages and input/output parameters. Semantics of an object/service is the meaning of the context, i.e. the ontology and value type for parameters. Semantics and context together identify the information and provide the meaning and syntax for the information that must be exchanged with the object/service for action. A web service implementation must include code for all contexts. If the context and semantics of the web service is not exposed then other applications will interface with the abstract form of the web service. This has following repercussions:
- The web service must be expanded every time a new context/semantics is to be added, e.g. new interface definition or new value type for parameter.
- A web service must perform the conversion function for context and semantic data.
The context of a web service will therefore describe the metadata required for an interface. When a web service is called by another web service in some context there has to be a conversion of metadata from calling web service context to the called web service context. This may also require semantic data conflict resolution and translation such as from one type value to another type value. If context and semantics are kept out of web service definition it will not only simplify the web service implementation but also can use a common standard metadata; a common context mediator may be used by other web services as well to resolve conversions and translations.
Example: Best 2Mbps DSL connection in cityname
| Context | Interface | Messages | Elements |
|---|---|---|---|
| 1 | Name DSL1; operation findDSLservice | GetDSLServiceInfo | Speed, Area (zipcode) |
| GetDSLServiceInfoResponse | Speed, Area (zipcode), Cost | ||
| 2 | Name DSL2; operation findDSLservice | GetDSLServiceInfo | Speed, Area (cityname, state) |
| GetDSLServiceInfoResponse | Speed, Area (cityname, state), Cost |
Call to GetDSLServiceInfo with standard context definition (metadata) will enable this message be sent to all web services that support this context and semantics for Speed (bitrate=Mbps) and Area. The user interface of the web application that has taken city & state as input parameters must convert it to the zipcode. This conversion may be built-in the web service (context 1) or done by a context mediator before forwarding the request to other web services that support zipcode (context 2).
| Subject | Predicate | Object |
|---|---|---|
| DSL broadband | Speed | 2Mbps |
| DSL broadband | Cost | _:currency |
| _:currency | Dollar | "value" |
| _:currency | Euro | "value" |
These web services may be supporting different semantics for elements in the message GetDSLServiceInfoResponse, the cost may be given in local currency. The cost is translated to the currency supported by the request sender web service by the context mediator. This reduces web service computing overhead and enables comparison of cost value in "open market".
Note: Read GetDSLServiceInfo for GetDSL in the figure. Reference: Maamar, Zakaria., Benslimane, Djamal. and Narendra, C. Nanjangud. What can context do for web services? Communications of the ACM. December 2006. 49(12), 98-103.
I am going to be blogging live from a couple of days of the 
Leave a comment