Database System Architecture Prof. Yin-Fu Huang CSIE, NYUST Chapter 2

Advanced Database SystemYin-Fu Huang 2.1Introduction A framework: ANSI/SPARC study Group on Data Base Management Systems

Advanced Database SystemYin-Fu Huang The three levels: (See Fig. 2.1) a. The internal level b. The external level c. The conceptual level 2.2The Three Levels of the Architecture

Advanced Database SystemYin-Fu Huang Example (Fig. 2.2)

Advanced Database SystemYin-Fu Huang The interrelationships (Fig. 2.3)

Advanced Database SystemYin-Fu Huang 2.3The External Level Data sublanguage vs. host language Tightly coupled vs. loosely coupled Data definition language (DDL) vs. Data manipulation language (DML) External view, external record, and external schema

Advanced Database SystemYin-Fu Huang 2.4The Conceptual Level Conceptual view, conceptual record, and conceptual schema. A great many additional features, such as the security and integrity constraints. 2.5The Internal Level Internal view, internal record, and internal schema The internal view is still at one remove from the physical level.

Advanced Database SystemYin-Fu Huang 2.6Mappings The conceptual/internal mapping The external/conceptual mapping The external/external mapping

Advanced Database SystemYin-Fu Huang The functions: a. defining the conceptual schema (logical database design) b. defining the internal schema (physical database design) c. liaising with users d. defining security and integrity constraints e. defining dump and reload policies f. monitoring performance and responding to changing requirements 2.7The Database Administrator

Advanced Database SystemYin-Fu Huang 2.8The Database Management System Procedures: a. A user issues an access request. b. The DBMS intercepts the request and analyze it. c. The DBMS inspects the external schema for that user, the external/conceptual mapping, the conceptual schema, the conceptual/internal mapping, and the storage structure definition. d. The DBMS executes the necessary operations on the stored database.

Advanced Database SystemYin-Fu Huang The functions (Fig. 2.4) a. Data definition b. Data manipulation Planned requests vs. unplanned requests c. Optimization and execution d. Data security and integrity e. Data recovery and concurrency (transaction manager) f. Data dictionary g. Performance

Advanced Database SystemYin-Fu Huang 2.9Data Communications The DC manager is not part of the DBMS but is an autonomous system in its own right. Database/data-communications system

Advanced Database SystemYin-Fu Huang 2.10Client / Server Architecture A server (the backend) and a set of clients (frontends) (See Fig. 2.5) Applications a. user-written applications b. vendor-provided applications (tools) The possibility arises of running clients and servers on different machines.

Advanced Database SystemYin-Fu Huang 2.11Utilities Utilities: a. Load routines b. Unload/reload routines c. Reorganization routines d. Statistical routines e. Analysis routines

Advanced Database SystemYin-Fu Huang 2.12Distributed Processing The DBMS backend on one machine and the application frontends on another. (See Fig. 2.6) Many arguments in favor of such a scheme: a. parallel processing b. server ⇒ a database machine c. client ⇒ a personal workstation d. A single database might be shared across several distinct client systems. (See Fig. 2.7)

Advanced Database SystemYin-Fu Huang One server machine, many client machines (Fig. 2.7)

Advanced Database SystemYin-Fu Huang A distributed database system (Fig. 2.8)

Advanced Database SystemYin-Fu Huang 2.12Distributed Processing (Cont.) User accesses can basically be provided in two different ways: a. A given client might be able to access any number of servers, but only one at a time. The user in such a system has to know which particular machine holds which pieces of data. b. The client might be able to access many servers simultaneously. The servers look to the client as if they were really a single server, and the user does not have to know which machines hold which pieces of data.

Advanced Database SystemYin-Fu Huang The End.