Chapter 2 IS 230 - King Saud University College of Computer...

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27/12/1437 >#< 1 Introduction to Database Systems Fall 2016 Dr. Ahmed Emam [email protected] [email protected] King Saud University College of Computer and Information Sciences Department of Information Systems Database System Concepts and Architecture
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27/12/1437 >#< 2 Chapter 2 Outline Data Models, Schemas, and Instances Three-Schema Architecture and Data Independence Database Languages and Interfaces The Database System Environment Centralized and Client/Server Architectures for DBMSs Classification of Database Management Systems Data Models Data Model: A set of concepts to describe the structure of a database, the operations for manipulating these structures, and certain constraints that the database should obey. Data Model Structure and Constraints: Constructs are used to define the database structure Constructs typically include elements (and their data types ) as well as groups of elements (for example, entity, record, table ), and relationships among such groups Constraints specify some restrictions on valid data; these constraints must be enforced at all times
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27/12/1437 >#< 3 Data Models Data Model Operations: These operations are used for specifying database retrievals and updates by referring to the constructs of the data model. Operations on the data model may include basic model operations (e.g. generic insert, delete, update) and user-defined operations (for example, compute_student_gpa, update_inventory) Categories of Data Models 1. Conceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.) 2. Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer. These are usually specified in an ad-hoc manner through DBMS design and administration manuals 3. Implementation (representational) data models: Provide concepts that fall between the above two, used by many commercial DBMS implementations (for example, relational data models used in many commercial systems).
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27/12/1437 >#< 4 Categories of Data Models Cont. Physical data models Describe how data is stored as files in the computer Access path Structure that makes the search for particular database records efficient Index Example of an access path Allows direct access to data using an index term or a keyword Some Terminology Entity : Represents a real-world object or concept Attribute Represents some property of interest Further describes an entity Relationship among two or more entities Represents an association among the entities Entity-Relationship model Relational data model Used most frequently in traditional commercial DBMSs Object data model New family of higher-level implementation data models Closer to conceptual data models
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27/12/1437 >#< 5 Schemas vs Instances Database Schema is the description of a database.
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