Transcript CH02

Chapter 2
Database System Architecture
Prof. Yin-Fu Huang
CSIE, NYUST
2.1 Introduction
 A framework: ANSI/SPARC study Group on Data
Base Management Systems
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2.2 The Three Levels of the Architecture
 The three levels: (See Fig. 2.1)
a. The internal level
b. The external level
c. The conceptual level
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Example (Fig. 2.2)
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The interrelationships (Fig. 2.3)
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2.3 The 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
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2.4 The Conceptual Level
 Conceptual view, conceptual record, and conceptual schema.
 A great many additional features, such as the security and
integrity constraints.
2.5 The Internal Level
 Internal view, internal record, and internal schema
 The internal view is still at one remove from the physical level.
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2.6 Mappings
 The conceptual/internal mapping
 The external/conceptual mapping
 The external/external mapping
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2.7 The Database Administrator
 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
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2.8 The 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.
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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
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2.9 Data Communications
 The DC manager is not part of the DBMS but is an
autonomous system in its own right.
 Database/data-communications system
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2.10 Client / 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.
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2.11 Utilities
 Utilities:
a. Load routines
b. Unload/reload routines
c. Reorganization routines
d. Statistical routines
e. Analysis routines
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2.12 Distributed 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)
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One server machine,
many client machines (Fig. 2.7)
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A distributed database system (Fig. 2.8)
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2.12 Distributed 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.
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The End.
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