chapter 2 database system architecture. an “architecture” for a database system. a specification...
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Chapter 2
Database System Architecture
An “architecture” for a database system.
A specification of how it will work, what it will “look like.”
The “ANSI/SPARC” architecture provides a model for a general description of database concepts.
Study Group on Database Management
Systems
National Committee on Information
Technology Standards (NCITS)
American National Standards Institute (ANSI)
Standards Planning and Requirements Committee
(SPARC)
Report “DBMS Framework”
1972, 1978
“ANSI”
“ANSI/SPARC” Architecture
“ANSI/SPARC”
“X3”
The Architecture
• Three “levels” of the architecture:
– Internal: How it is physically stored.– External: How it is used, what does it “look
like” to the user (a user).– Conceptual: An abstract specification--
how does it “look” in general, in its entirety.
Fig. 2.1 The three levels of the architecture
Fig. 2.1 The three levels of the architecture
User 1 User 2 User n Each user (or user program) has a different, and partial view of the data.
The “view” of the entire database (as seen by the designer(s) and DBA.
How the data is actually (physically) stored.
Internal level, physical level: the way the data is actually stored.
External level, user logical level: the way the data is seen by each individual user or user program.
Conceptual level, community logical level: the logical view of the entire data structure. Definitions only--no consideration of how used or stored.
External: (Java)
class Employee { String employeeNumber; String departmentNumber; float salary;
} Conceptual: Employee Employee_Number char (6) Department_Number char (4) Salary numeric(5) Internal:
STORED_EMP LENGTH = 18 PREFIX TYPE=BYTE(6), OFFSET=0 EMP# TYPE=BYTE(6), OFFSET=6, INDEX=EMPX DEPT# TYPE=BYTE(4), OFFSET=12, PAY TYPE=FULLWORD, OFFSET=16
Same data, different names
The DBMS ties it all together
At the external level, application programs are written in Java, C++, COBOL, PL/1, Ada, or … (the “host” language).
A data sublanguage is embedded in or interfaced with the program, or used interactively with the DBMS.
The data sublanguage (DSL) of the DBMS is almost universally SQL.
Fig. 2.3 Detailed system architecture
The DBMS provides:
Data Definition Language (DDL)
for the internal
external “schemas”
conceptual
The schemas (plans) are the definitions of how the data is to be stored and how it is to be viewed.
The DBMS provides:
Data Manipulation Language (DML)
for “planned” use
“unplanned” use
.
Planned: operational, production
Unplanned: ad hoc queries, DSS
Embedding:
PL/1 program, DB2 DBMS, DB2-PL/1 pre-compiler
Interfacing:
Java program, any DBMS, JDBC interface
DBMS provides for:
Data Definition
Data Manipulation
Query Capability
with a program or interactively
interactively
SQL is usually the language for all of these
The DBMS provides:
Security enforcement
Integrity checks
Recovery
Concurrency control
Transaction management
Data dictionary
Performance optimization
Data Dictionary
Catalog synonyms
Repository
The “metadata”--data about the data--part of the database (itself a database).
Fig. 2.4 Major DBMS Functions and Components
Logical to Physical Mapping
file
file block disk
block
total disk
space
disk
record 142record 142
record 142record 142
record 142
Logical to Physical Mapping
file
file block disk
block
total disk
space
disk
record 142record 142
record 142record 142
record 142
a table,
part of a table,
multiple tables
Access Methods
• Sequential Access
• Direct Access
• Indexed Access
Access Methods
• Sequential Access
read next write next (append)
(typically either read existing file or write new one)
rewind (go back to the beginning)
generally no read after write
may be able to skip ahead or back
Sequential-access File
Access Methods
• Direct Access– Relative Access, Random Access
read n write n
or, position to n read next write next
(n = relative block number)
must know n (e.g., n is employee number) or calculate n (e.g., n is hashed from employee name)
Access Methods
• Indexed Access
use of an index to find what n is
index is itself a file
if small, can be read and kept in memory
if large, can have an index to the
blocks of the large index
Example of Index and Relative Files
Access Methods
• Sequential Access vs. Direct Access
– Sequential preferable when entire file is to be accessed
– Direct access preferred when access is needed to a few records
– Application determines– Both may be desirable—more difficult to
achieve
The DBMS vendor provides utilities for:
Loading the database (from files).
Unloading/reloading the database for backup.
Reorganization (to improve performance).
Gathering statistics (on usage or performance).
Statistical analysis.
Client/Server Architecture
Fig. 2.5 Client/server architecture
Backends and Frontends
CPUDatabase Network, Users
“backend”
(DB manager)
“frontend”
(DC manager)
“back” “front”
Distributed Processing
Fig. 2.6 Client and server running on different machines
Backends and Frontends
NetworkServer
(DBMS)Client
“backend” “frontend”
Fig. 2.7 One server machine, many client machines
Distributed processing, centralized database
Fig. 2.8 Each machine runs both client(s) and server
Distributed database
“Two-tier” Systems
Application Server
Database Server
Client
same or different computers
network
networkServer
(DBMS)Client
Application Server
Database Server
Client
network
“fat” client
“thin” client
2.2 Define the following terms:
back end front end
client host language
conceptual DDL, schema, view load
conceptual/internal mapping logical database design
data definition language internal DDL, schema, view
data dictionary physical database design
data manipulation language planned request
data sublanguage reorganization
DB/DC system server
DC manager storage structure definition
distributed database unload/reload
distributed processing unplanned request
external DDL, schema, view user interface
external/conceptual mapping utility
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