the blueprint of any database system is the schema.
the blueprint of any database system is the?
schema
the database schema of a database system is its structure described in a formal language supported by the database management system (dbms). the term "schema" refers to the organization of data as a blueprint of how the database is constructed (divided into database tables in the case of relational databases). the formal definition of a database schema is a set of formulas (sentences) called integrity constraints imposed on a database. these integrity constraints ensure compatibility between parts of the schema. all constraints are expressible in the same language. a database can be considered a structure in realization of the database language. the states of a created conceptual schema are transformed into an explicit mapping, the database schema. this describes how real-world entities are modeled in the database.
database schema
a database system in a multidatabase environment is assumed. from a software architecture point of view a co component that implements the generic co algorithm locally, the "commitment order coordinator" (coco), can be designed in a straightforward way as a mediator between a (single) database system and an atomic commitment protocol component (raz 1991b). however, the coco is typically an integral part of the database system. the coco's functions are to vote to commit on ready global transactions (processing has ended) according to the local commitment order, to vote to abort on transactions for which the database system has initiated an abort (the database system can initiate abort for any transaction, for many reasons), and to pass the atomic commitment decision to the database system. for local transactions (when can be identified) no voting is needed. for determining the commitment order the coco maintains an updated representation of the local conflict graph (or local augmented conflict graph for capturing also locking deadlocks) of the undecided (neither committed nor aborted) transactions as a data structure (e.g., utilizing mechanisms similar to locking for capturing conflicts, but with no data-access blocking). the coco component has an interface with its database system to receive "conflict," "ready" (processing has ended; readiness to vote on a global transaction or commit a local one), and "abort" notifications from the database system. it also interfaces with the atomic commitment protocol to vote and to receive the atomic commitment protocol's decision on each global transaction. the decisions are delivered from the coco to the database system through their interface, as well as local transactions' commit notifications, at a proper commit order. the coco, including its interfaces, can be enhanced, if it implements another variant of co (see below), or plays a role in the database's concurrency control mechanism beyond voting in atomic commitment.
commitment ordering