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Database Systems 본문
DBMS supports database languages that allow users to express what they want to do with database
QUEL, SQL, relational algebra, query-by-example, LDL, etc.
Application programs generally access databases through
-procedural extension of SQL
-embedding SQL in host program languages
-application program interface (e.g. ODBC/JDBC)
DBMS Components
-two key components(query processor, storage manager)
1.query processor : query processing, authorization, authentication etc.
2.storage manager : efficient storing(retrieving and updating of data), file organization(Indexing and hashing), transaction management, etc.
simplified database system
user1,2.... n <=> application 1,2,..., n <=> DBMS servers(query processor <->storage manager)<=> DB, meta data(데이터에 관한 구조화된 데이터, 속성 정보라고도함)
Data dictionary
Data dictionary contains metadata(i.e. data about data)
-Data schema(데이터 스키마), Integrity constraints(무결성 제약), Authorization(접근권한), Statistical data
스키마는 DB의 구조와 제약 조건에 관한 전반적인 명세를 정의한 메타데이터의 집합
DBMS references data dictionary to process database languages
Transaction Management
-sequence of database operations that performs a single logical function in database applications
-transaction management has two components(concurrency control, recovery manager)
concurrency control manger controls the interation among the concurrent transactions to ensure the consistency of the database
-recovery manager ensures that the database remains in a consistent(correct) state despite of failures
Database users(differentiated by the way they expect to interact with the system)
1.naive users
-invoke one of the permanent application programs that have been wirtten previously
2.app programmers
3.database designer
4.database analysts
5.database administrator(DBA)
Database Administrator(DBA)
-coordinates all the activities of the database system
-database administrator's duties(schema def,storage stucture&acces method def, schema&physical organization modification, authorization of users to acces databases, specifying integrity constraints, acting as liaison with users, monitoring system performance etc.)
Database System Architecture
-architecture of a database systems is influenced by the underlying computer system on which the database is running
Centralized, Distributed, Client-server,parallel(multi-processor)