Cornell & CNRI: open architecture, confederated DLs, goal of interoperability & extensibility. Allows flexible interaction of existing services & augmentation of the infrastructure with new services.
Interoperability: broad problem domain. typically investigated w/in specific scope (comminity, classification of info, IT area, etc)
- creating a general framework for info access & integration across domains
- goal to enable communities w/ different info & tech to achieve general level of info sharing
Definition: ability of DL components of services to be functionally & logically interchangeable by virtue of their having been implemented in accordance with a set of well-defined, publically known interfaces.
some approaches:
1) standardization
2) distributed object request architectures (eg COBRA)
3) remote procedure calls
4) mediation
5) mobile computing
Cornell/CNRI approach:
1) agreement on common abstractions
2) definition of open interfaces to services/components that implement the abstractions
3) creation of extensibility mechanism for introducing new functionality into arch w/out interfering w/ core interoperability
Principle abstractions:
1) repository: different content managed in uniform manner
2) Digital Object: datastreams/elements (MIME sequence in bytes)
3) Disseminator: extend behavior of DOs & enable interaction
4) AccessManager
Disseminator Types: set of op's that extends basic functionality of a DO. (book - "get next page" "translate text" etc)
- signatures
- DOs can be used to make diss types avail in interface
Servlets: executable program capable of performing the set of op's defined for specific diss types.
- equivalence achieved when diff servlets operate on diff types of underlying datastreams to produce equivalent results.
- stored & registered in infrastructure in uniquely named DO
Extensibility: key is clean seperation of object structre, diss types, & mechanisms taht implement extended functionality.
- can endow DO w/ additional functionality
- new interfaces can be added
Interoperability Experiments:
- IT0: Protocol & Syntactic Interoperability
-IT1: Functional & Semantic
- 1.1: DO Access
- 1.2: DO Creation
- 1.3 Extensible Access
- IT2: Interoperability of Extensibility Mechanisms.
- 2.1: Ability to dynamically load signatures & servlets
- 2.2: Demonstrate flexibility w/ which new diss types are dynamically added to infrastructure
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