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1、70420403- Database Systems 数据库管理系统,Li J,References,Raghu Ramakrishnan/Johannes Gehrke, Database Management Systems, 2nd Ed. , 清华大学出版社/McGraw-Hill, 2000 C. J.Date, 数据库系统导论（第7版）, 机械工业出版社,What is DBMS?,Need for information management A very large, integrated collection of data. Models real-world enterp
2、rise. Entities (e.g., students, courses) Relationships (e.g., Liu Wei is taking 70420403) A Database Management System (DBMS) is a software package designed to store and manage databases.,Why Use a DBMS?,Data independence and efficient access. Data integrity and security. Uniform data administration
3、. Concurrent access, recovery from crashes. Replication control Reduced application development time.,Database Management,Why Study Databases?,Shift from computation to information at the “low end”: access to physical world at the “high end”: scientific applications Datasets increasing in diversity
4、and volume. Digital libraries, interactive video, Human Genome project, e-commerce, sensor networks . need for DBMS/data services exploding DBMS encompasses several areas of CS OS, languages, theory, AI, multimedia, logic,?,Database Systems,Key Terms cont.,Database System A database, a database mana
5、gement system and appropriate hardware and personnel.,Database System: Hardware,Set of physical devices on which a database resides. It consists of one or more computers, disk drives, CRT terminals, printers, tape drives, connecting cables and other auxiliary and connecting hardware.,Database System
6、: Hardware cont.,Database System: Software,A database software includes two types of software General-purpose database management software, usually called the database management system (DBMS) Application software that uses DBMS facilities to manipulate the database to achieve a specific business fu
7、nction, such as providing reports or documents, which can be used by users.,Database System: Software cont.,Application software is generally written standard programming language such as C, or it may be written in a language (commonly called a fourth-generation language) supplied with the DBMS. The
8、se programs utilise the command language of the DBMS and make use of the information contained in the data dictionary.,Database System: Software cont.,User Interface Language, menus and other facilities by which users interact with various system components, such as application programs, the DBMS Co
9、mputer-aided software engineering (CASE) tools Automated tools used to design databases and application programs.,Data Dictionary/Directory (Repository),A subsystem that keeps track of the definitions of all data items in the database. relationships that exists between various data structures. index
10、es that are used to access data quickly. screen and report format definitions that may be used by various application programs.,Data Dictionary,Definitions of data items in the database includes: Elementary-level data items (fields), group and record-level data structures, and files or relational ta
11、bles.,Data that describe the properties or characteristics of other data. Some of these properties include data definitions, data structures and rules or constraints. Item name, the data type, length, minimum and maximum allowable values (where appropriate) and a brief description of each data item.
12、 Metadata allow database designers and users to understand what data exist, what the data mean. Data without clear meaning can be confusing, misinterpreted or erroneous.,Metadata,E.g. Data ItemValue NameTypeLengthMin MaxDescription NameCharacter30Employee Name IDNumber9Employee No. DeptCharacter10De
13、pt. No. AgeInteger218 60Employee Age NameCharacter15Dept. Name ManagerNumber9Mgr. Emp. No. Employee No. (ID) unique Manager is an employee of the organisation,Metadata,Database System: People,Two different types of people (users and practitioners) are concerned with the database. Users who need info
14、rmation from the database to carry out their primary business responsibility e.g. Executives, managers, staff, clerical personnel,Database System: People cont.,Practitioners people responsible for the database system and its associated application software. e.g. Database administrators, analysts, pr
15、ogrammers, database and system designers, information systems managers.,Components of a Database System,Four components: People, H/W, S/W, Data Practitioners (analysts and database designers) in consultation with users identify data needs and design database structures to accommodate these needs. Th
16、e database structures are specified to the DBMS through the data dictionary.,Components of a DBS cont.,Users enter data into the system by following specified procedures. The entered data are maintained on hardware media such as disks and tapes. Application programmes that access the database are written by practitioners and users to be run on computers.,Components of a DBS cont.,Key Terms cont.,Database Management System Systems software that facilitates the management of a database.
