chapter 21 chapter 2 database system concepts and architecture
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Chapter 2 1
Chapter 2Database System Concepts
andArchitecture
Chapter 2 2
Data Models
• A data model is a description of the structure of a database. Data models generally, fall into 3 categories according to the level of the description.
Chapter 2 3
• High-level ( or conceptual) data models closely approximate the miniworld.
• Representational ( or, implementational ) data models are intermediate data models close to the miniworld but also reflecting the actual organization of data in the database.
• Low-level ( or, physical) data models describe details of physical storage, generally transparent to casual or parametric end users.
Chapter 2 4
• A data model is often specified by a database schema typically displayed in a schema diagram that consists of schema constructs.
Chapter 2 5
University Database SchemaDiagram
• fig 2.1
Chapter 2 6
Database State
• The actual data in a data base at a particular instant is the database state, which consists of a set of instances for each schema construct.
• Defining a database consists of specifying a schema to the DBMS. We then have a database in an empty state, with no data.
Chapter 2 7
• When data is first loaded, the database is in its initial state.
• Subsequently, each update creates another state. The DBMS must guarantee that each such state is a valid state that satisfies schema specifications.
• The schema is the intension, while a database state is the extension of the schema.
Chapter 2 8
ExternalView1
ExternalView1
Conceptual Schema
Internal Schema
External/High Level
Chapter 2 9
DBMS Languages
• DDL - Data Definition Language is used to define both schemas.
• VDL - View Definition Language is used to specify the mapping of the user views to the conceptual schema.
• DML - Data Manipulation Language is used to provide a means to manipulate the database. (I.e. insert, delete, query,etc)
Chapter 2 10
• Most DBMS’s combine the various capabilities of the DDL, VDL, DML and SDL into a single high-level DML (e.g. SQL relational database language.)
• Such DML’s can generally be entered interactively from the terminal or embedded in a high-level language such as C which acts as a host language.
Chapter 2 11
Common Approaches by Users
• Typically, sophisticated end users embed the DML .
• Casual end users usually access interactively through user-friendly interfaces created by too developers– Menu based interfaces– Graphical interfaces– Forms base interfaces
Chapter 2 12
• Parametric end users are provided with tailored interfaces for canned transactions that are designed by a systems analyst.
Chapter 2 13
Components of a DBMS
• fig 2.3
Chapter 2 14
Database System Utilities
• Loading
• Conversion
• Backup
• File Reorganization
• Performance monitoring
• Communication
Chapter 2 15
Database Classifications
• Single-user vs. Multiuser
• Centralized vs. Distributed
• Data Model– Relational– Network– Hierarchical– Object-oriented
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