Chapter 2 Database System Concepts and Architecture Chapter

Chapter 2 Database System Concepts and Architecture Chapter 2 1

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 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 3

• A data model is often specified by a database schema typically displayed in a schema diagram that consists of schema constructs. Chapter 2 4

University Database Schema Diagram • fig 2. 1 Chapter 2 5

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 6

• 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 7

External /High Level External View 1 Conceptual Schema Internal Schema Chapter 2 8

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 9

• 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 10

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 11

• Parametric end users are provided with tailored interfaces for canned transactions that are designed by a systems analyst. Chapter 2 12

Components of a DBMS • fig 2. 3 Chapter 2 13

Database System Utilities • • • Loading Conversion Backup File Reorganization Performance monitoring Communication Chapter 2 14

Database Classifications • Single-user vs. Multiuser • Centralized vs. Distributed • Data Model – Relational – Network – Hierarchical – Object-oriented Chapter 2 15