DATABASE SYSTEMS (phần 26) pot

... trẻ sử dụng một tay nào đó để làm mọi việc. Có một số trẻ thuận cả hai tay cho đến 5-6 tuổi và sau đó tự chúng sẽ chọn lựa chúng thích sử dụng tay nào hơn. Số người thuận tay trái trên thế ... thuận tay nào bị ảnh hưởng lớn bởi yếu tố di truyền. Nếu cả hai vợ chồng đều thuận tay trái thì đứa trẻ có 42% khả năng cũng sẽ thuận tay trái. Và nếu bạn tò mò muốn biết trẻ thuận...

Ngày tải lên: 02/07/2014, 04:20

... 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

... databases and Web pages. XML combines concepts from the models used in document systems with database modeling concepts. 1.7.5 Extending Database Capabilities for New Applications The success of database systems in traditional applications ... processing and optimization, their performance improved. Eventually, relational databases became the dominant type of database systems fo...

Ngày tải lên: 07/07/2014, 06:20

... concepts (see Chapter 24). • KR schemes include reasoning mechanisms that deduce additional facts from the facts stored in a database. Hence, whereas most current database systems are limited to ... relational database and a rela- tional database schema. A relational database schema S is a set of relation schemas S = (R I , R z , , R m } and a set of integrity constraints IC....

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 ... whose DNUM = 5. We can therefore write: IF (x.DNUM =5) THEN F z which is equivalent to (NOT (x.DNUM =5) OR F z ) 3. Formula F I , hence, is of the form NOT(x.DNuM =5) OR...

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

... appropriate SQL DDL statements to define the database. 8.8. Repeat Exercise 8.7, but use the AIRLINE database schema of Figure 5.8. 8.9. Consider the LIBRARY relational database schema of Figure 6.12. Choose the appro- priate action (reject, ... updating, and the specification of views. Most database systems have an interactive interface where these SQL commands can be typed directl...

Ngày tải lên: 07/07/2014, 06:20

... a constraint between two sets of attributes from the database. Suppose that our relational database schema has n attributes AI' A 2 , ••• , An; let us think of the whole database as being described by a single universal relation ... { 6) System.out.println ("Driver could not be loaded") ; 7) } 8) String dbacct, passwrd, ssn, lname 9) Double salary ; 10) dbacct = readent...

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

... discussing the role of information systems in organizations; database systems are looked upon as a part of information systems in large-scale applica- tions. We discussed how databases fit within an information ... and 11) discuss high level transaction design and joint analysis of data and functions. Shasha (1992) is an excellent source on database tuning. Information about some...

Ngày tải lên: 07/07/2014, 06:20

... (see Chapter 6). Practical Database Design and Tuning In this chapter, we first discuss the issues that arise in physical database design in Section 16.1. Then, we discuss how to improve database performance through database tuning in Section ... undertaking physical database design, we must have a good idea of the intended use of the database by defining the queries and transacti...

Ngày tải lên: 07/07/2014, 06:20

... in a database. Because part of the theoretical foundation for some deductive database systems is mathematical logic, such rules are often referred to as logic databases. Other types of systems, ... in the application programs that access the database. Section 24.3 will give a brief overview of spatial and multimedia databases. Spatial databases provide concepts for databases that kee...

Ngày tải lên: 07/07/2014, 06:20

... types of distributed database systems, including federated and multidatabase systems and highlights the problems of heterogeneity and the needs of autonomy in federated database systems, which will ... retrieve the employee 25.7 Distributed Databases in Oracle I831 Net8 Database server Database server Net8 (c:::>c:::>c:::> = EMPtable t- , , Sales , database CONNECT T...

Ngày tải lên: 07/07/2014, 06:20

... 262 sequence interaction, 263-264 database programming languages, 255 database schema, 27-28, 115 database servers, 36, 263 database state, 28 database systems active, 19 active database technology, 3 characteristics, 8-11 deductive, ... data, 902 database administrators (DBA), 12 interfaces for, 34 security and, 734 database applications, 49, 52-53, 255, 262 database desi...

Ngày tải lên: 07/07/2014, 06:20

... 308 11 .3 Minimizing I/O Cost versus Number of I/Os 309 11 .3 .1 Blocked I/O 310 11 .3.2 Double Buffering 311 11 .4 Using B+ Trees for Sorting 312 11 .4 .1 Clustered Index 312 11 .4.2 Unclustered Index 313 11 .5 ... Replication 611 21. 8 Distributed Catalog Management 611 21. 8 .1 Naming Objects 612 21. 8.2 Catalog Structure 612 21. 8.3 Distributed Data Independence 613 2...

Ngày tải lên: 08/08/2014, 18:22