Abstract: Routing information is exchanged between edge routers in different autonomous systems that independently define their routing policies. A Simple Path Vector Protocol extends the prior art Border Gateway Protocol in a manner that is guaranteed to converge by adding a new attribute to the routing messages sent by an edge router to its peers in the different systems. This attribute is a path history, which is dynamically computed at each router as the routing path to a particular destination is changed. The path history attribute is sent in a routing message by a router to its peers together with the sending router's path to that destination. By observing the dynamic path history that is computed at a router as a received routing message from a peer router that contains a history attribute is processed, a cycle can be identified in the newly computed history and associated with a policy conflict at that receiving router's associated autonomous system.

Abstract: A logical data architecture for fetch-intensive database applications includes a first and a second logical database. The second database includes materialized views over the first database. Updates are propagated from the first database to the second database using so-called view maintenance techniques. In preferred embodiments, the first database may be optimized for update transactions and the second database may be optimized for read transactions. At least one of the materialized views included in the second database is based on a pre-defined application read transaction. The update processing overhead associated with view maintenance is substantially performed at the first database.

Abstract: A hypothetical query in a database system is transformed using algebraic equivalences involving explicit substitutions so as to produce one or more equivalent queries which can be evaluated more efficiently than the original hypothetical query. The hypothetical query may be of the form Q when {U} where Q is a relational algebra query and U is an update expression. The value assigned to the hypothetical query in a database state DB is the value that Q would return in the database state reached from DB by executing update U. One or more explicit substitutions are used to represent hypothetical database state changes, and algebraic equivalences involving the explicit substitutions are applied to the hypothetical query in order to generate at least one additional query which is equivalent to the hypothetical query. Several equivalent queries may be generated, and their estimated computation times compared, in order to select a particular equivalent query for direct evaluation.

Abstract: Apparatus and methods for reducing the amount of computation required to determine the consequences of a side effect resulting from a transaction on a relation in a data base system. The apparatus and methods use equational reasoning based on a bag algebra representation of a class of transaction and the relation to produce a pre-expression which describes the side effect. The pre-expression is included in the data base system's data dictionary, and when a transaction of the class is received in the data base system, the pre-expression is used to determine the side effect. The pre-expression is formed with a strongly-minimal pair of delete and insert bags. The apparatus and methods may be used to maintain materialized views, to check for violation of constraints on the data base, and to activate triggers, monitors, and active queries.

Abstract: A technique which may be used in a transaction which updates a data set when the data set is subject to constraints and includes operations which may abort. The technique produces an update constraint which may be tested before the data set is altered to determine whether the constraints will be satisfied if the data set is altered. The update constraint of the technique indicates whether the constraints would be satisfied if the transaction could not abort. The update constraint is checked at the application level, while the constraints which cause an operation to abort are checked at the system level. An application of the update constraint to a relational data base embedded in a telephone switch is disclosed.