Yunsheng Liu

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• Yunsheng Liu
• 2008.9

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2.1 Data and Their Representation

• 2.1.1 Data and Information

1. Data
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2.1.1 Data and Information
2. Information - Information is processed and
refined data which is used in decision
making.
3. Data vs. Information (1). Information is
made up of two parts ? data
? context (2). Sometimes, they are
exchangeable to use (3). Relations and
differences
4. Knowledge
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2.1.1 Data and Information
Examples
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2.1.2 Data Representations
- The use of a DBS is ultimately concerned
with some real-word enterprise, and the
data to be stored describes various
aspects of this enterprise.
1. Three realms

• Real-world,
• Data/information-world
• Computer-world

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• Relationships among the three worlds

Physical Phenomena
Operating
Understanding
Strategies, Rules
KNOW.
Observing
Extracting
Relating
INFOR.
Representing
DATA
Expiaining
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2.1.2 Data Representations
2. Types vs. occurrences of data
The Type of STDUDENT
STUDENT
Student S-Name Sex Birthday Dept.
2008101001 Wei Liu M 1990-10-01 SW


An occurrence of STDUDENT

• Entities
• - An entity is a thing/object in the RW which
  exists and is
• distinguishable from any others

objective or subjective
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2.1.3 Relationships Between Data
1. Relationships between data items ?
Represanting semantic dependencies between
data items ? Used to aggregate the related
data items into entities ? The types
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2.1.3 Relationships Between Data
2. Relationships between record types ?
Conceptrepresenting semantic relations between
two entity sets/classes ?
Purposemodeling the relations among entity
types ? Semantic notions e.g.

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2.1.3 Relationships Between Data
3. Relationship types between record types -
Defined by the numbers of record occurrences for
each record type to appear in a
rerlationship
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2.2 Data Views
2.2.1 Hierarchical Data Abstractions

• 1. Abstraction at physical level
• - Describing physical data structure while
  hiding storage device properties and
  operational details
• 2. Abstraction at conceptual/logical level
• - Describing total logical data structure
  while hiding physical structures and
  Implementation details
• 3. Abstraction at user level
• - Describing local logical data structures
  for various users while hiding total structure
  complexity and details

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2.2.2 Hierarchical Data Views
- Various data structures observed by different
kinds of users taking different stands on and
with different viewpoints

1. End-user views I/O formats
2. Applications views local logical structures
3. System view total logical structure
4. Storage view storage structure
5. Physical view physically organizing structure on
   a storage device

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2.2.3. Database Schemas

• A formal specification of a database structures
  (design or plan) in the DDL of a DBMS

1. Subschemas / External schema

• A formal specification of a local logical
  structure of a DB used by a user/application
• There are many subschemas for a DB

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2.2.3. Database Schemas

1. Conceptual/Logical schema

• A formal specification of a total logical
  structure of a entire DB.
• A schema is an integration of all the subschemas.
  
• Each subschema can be derived from the conceptual
  schema and permitted to have some differences

1. Stored/Internal schema

• A formal specification of a total physical
  structure or file organization of an entire DB.

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2.2.4 Independencies of Data

• Data independence means that a data specification
  is separated( independent) from its use(
  program).
• There are two kinds of data independences

• Physical data independence
• - The physical schema can be changed without
  altering the conceptual schema or redefining
  subschemas and in turn rewriting application
  programs
• Logical data independence
• - The conceptual schema can be modified
  without affecting application programs

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Database System Hierarchy
Conceptual schema
Stored schema
2.2 H-Abstrac
2.2.2 Hierarchical Data Views
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2.3 Introduction to Data Models
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2.3 Introduction to Data Models
3. Three classical data models ?
Hierarchical model ? Network model ?
Relational model 4. Semantic data models

• E-R, the 1th SDM
• Function model, Role model, Type model, etc.

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2.4 Database Languages

1. Introduction

• Syntax language text
• Processing Compiler system
• Two kinds of capabilities

• Algebraic operatingas a general programming
  language,
• Accesses to a DB

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2.4 Database Languages
2. Data language ? DDL Data
definition/description language ? DML Data
manipulation language ? QL Query language

• 3. DBCL Database control language
• HL Host Language, a programming language
  within which DML statements can be
  embedded

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2.4 Database Languages
5. The language utilization
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2.5 Database Organization

• Hierarchy of DB Organization

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2.6 Queries

• The essential purpose to develop a DB is for
  conveniently utilizing the DB
• Two kinds of operations query and maintenance
  and a query is more complex than others
• Query processing includes

• Q specification in QL ? physical DB operations
• Optimizations
• Execution

• It has a heavy influence on the performance of
  the system

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2.7 Transaction Management

• - Transaction Management is the core and key
  issue
• of a DBS
• Admission
• Resource management CPU, I/O and buffer, data
• Consistency maintenance
• Execution control
• Recovery management

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2.8 Database Users

1. User types

• End-users

• Occasional
• Repeat-based
• IP professionals

• Operators
• Application programmers
• Database Administrators/Developer
• System programmers

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1. The Relationships among users

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2.9 Database System Architecture