http://dl.acm.org/citation.cfm?id=4233
An approach to the coordinated sharing and interchange of computerized information is described emphasizing partial, controlled sharing among autonomous databases… A federation consists of components (of which there may be any number) and a single federal dictionary.
The components represent individual users, applications, workstations, or other components in an office information system. The federal dictionary is a specialized component that maintains the topology of the federation and oversees the entry of new components. Each component in the federation controls its interactions with other components by means of an export schema and an import schema. The export schema specifies the information that a component will share with other components, while the import schema specifies the nonlocal information that a component wishes to manipulate.
The federated architecture provides mechanisms for sharing data, for sharing transactions (via messagetypes) for combining information from several components, and for coordinating activities among autonomous components (via negotiation).
The goal of this paper is to define an architecture and supporting mechanisms for interconnecting databases that minimizes central authority, yet supports partial sharing and coordination among database systems. This feder- ated database architecture [10, 12, 13] allows a collection of database systems (components) to unite into a loosely coupled federation in order to share and exchange information.
Without the constraint of a central authority, the mechanisms provided for the federated architecture must balance two conflicting requirements: the components must maintain as much autonomy as possible; however, the components must be able to achieve a reasonable degree of information sharing.
components represent individual information systems that wish to share and exchange information. Each federation has a single federal dictionary, which is a distinguished component whose information province is the federation itself.
A component has associated with it three schemas: the private schema, export schema, and import schema …
The private schema describes that portion of a component’s data that is local to (stored at) the component.
In addition to the application-specific data, the private schema contains a small collection of information and transactions relevant to the component’s participation in the federation. This information is exported by the component for use by other components, particularly the federal dictionary. The federation-specific information falls into three categories:
The import schema of a component specifies the information that component desires to use from other components.
… is the fundamental information-sharing operation in a federation.
(important to note that) the importation of a schema is separate from subsequent data access.
implicit contract is established between c1 and c2. In this contract c1 guarantees that it will not modify the definition (structure or semantics) of the exported element unless it notifies the importer. By this contract c2 also agrees to notify c1 when it no longer requires access to the element. This process of negotiated change is a key element of the federated architecture.
With the absence of a central authority, the federated architecture provides a mechanism to coordinate the sharing of information among components: the negotiation subsystem.
A negotiation is a multistep, distributed dialogue among two components.
negotiation is distinct from the process of data access. Negotiation establishes the right to accesssome general kinds of data elements.
Each negotiation procedure contains three elements: a set of participant schemas, a negotiation schema, and a negotiation graph.
To support the negotiation process, each participating component has a negotiation database.
The possible steps for each kind of negotiation are specified by the negotiation graph.
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