Chapter 2 Database System Concepts and Architecture

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

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

A data model is often specified by a database schema typically displayed in a schema diagram that consists of schema constructs. Chapter 2

University Database Schema Diagram fig 2.1 Chapter 2

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

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

External /High Level External External View1 View1 Conceptual Schema Internal Schema Chapter 2

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

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

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

Parametric end users are provided with tailored interfaces for canned transactions that are designed by a systems analyst. Chapter 2

Components of a DBMS fig 2.3 Chapter 2

Database System Utilities Loading Conversion Backup File Reorganization Performance monitoring Communication Chapter 2

Database Classifications Single-user vs. Multiuser Centralized vs. Distributed Data Model Relational Network Hierarchical Object-oriented Chapter 2