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

... 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

... 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

... 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

Ngày tải lên: 04/07/2014, 02:20

... using, and imple- menting database systems and applications. Our presentations stresses the fundamentals of database modeling and design, the languages and facilities provided by the database management systems, and system implementation techniques. The book is meant to be used ... I Chapter 1 Databases and Database Users DATABASE SYSTEM UserS/Programmers ~ Application Programs/...

Ngày tải lên: 07/07/2014, 06:20

... are becoming quite popular. These systems provide an environment for developing database applications and include facilities that help in many facets of database systems, including database design, CUI development, querying and ... processing and optimization, their performance improved. Eventually, relational databases became the dominant type of database systems for traditiona...

Ngày tải lên: 07/07/2014, 06:20

... additional facts from the facts stored in a database. Hence, whereas most current database systems are limited to answering direct queries, knowledge-based systems using KR schemes can answer queries that involve inferences over the stored ... relational database and a rela- tional database schema. A relational database schema S is a set of relation schemas S = (R I , R z , ,...

Ngày tải lên: 07/07/2014, 06:20

... as RM/T. Childs (1968) had earlier used set theory to model databases. Later, Codd (1990) published a book examining over 300 features of the relational data model and database systems. Since Codd's pioneering ... discuss JOIN and other complex binary operations, which operate on two tables. The COMPANY relational database shown in Figure 5.6 is used for our examples. Some common...

Ngày tải lên: 07/07/2014, 06:20

... success of rela- tional databases in the commercial world. Because it became a standard for relational databases, users were less concerned about migrating their database applications from other types of database systems- for example, network or ... 10 b 5 FIGURE 6.13 A database state for the relations T1 and T2. Relational Database Design by ER- and EER-to-Relational Mapping We now...

Ngày tải lên: 07/07/2014, 06:20