DATABASE SYSTEMS (phần 9) pps
DATABASE SYSTEMS (phần 9) pps
... a relational database schema for this database application. First show all the functional dependencies that should hold among the attributes. Then design relation schemas for the database that are each in ... becomes questionable when the constraints on which they are based are hard to understand or to detect by the database designers and users who must discover these constraints. Thu...
Ngày tải lên: 07/07/2014, 06:20
DATABASE SYSTEMS (phần 12) pps
... block accesses to find a specific record in a file with b blocks. Ordered files are rarely used in database applications unless an additional access path, called a primary index, is used; this results ... field. Such an organization is called an indexed sequential file and was used in a large number of early IBM systems. Insertion is handled by some form of overflow file that is merged per...
Ngày tải lên: 07/07/2014, 06:20
DATABASE SYSTEMS (phần 15) pps
... it contains several transaction boundaries. If the database operations in a transaction do not update the database but onlyretrieve data, the transaction is called a read-only transaction. The model of a database that is used ... completes execution without error or it fails and leaves the database unchanged. 554 IChapter 17 Introduction to Transaction Processing Concepts and Theory...
Ngày tải lên: 07/07/2014, 06:20
DATABASE SYSTEMS (phần 16) pps
... followed and undone. 19.6 RECOVERY IN MULTIDATABASE SYSTEMS So far, we have implicitly assumed that a transaction accesses a single database. In some cases a single transaction, called a multidatabase transaction, may ... Do Not Affect the Database In general, a transaction will have actions that do not affect the database, such as generat- ing and printing messages or reports from info...
Ngày tải lên: 07/07/2014, 06:20
