tailieunhanh - Lecture Fundamentals of database systems: Chapter 2 - Emasri, Navathe

In this chapter presenting the terminology and basic concepts that will be used throughout the lecture. This chapter discusses data models and defines the concepts of schemas and instances, which are fundamental to the study of database systems, discuss the three-schema DBMS architecture, provides a user’s perspective on what a DBMS is supposed to do, describe the types of interfaces and languages that are typically provided by a DBMS,. | Data Models and Their Categories History of Data Models Schemas Instances and States Three-Schema Architecture Data Independence DBMS Languages and Interfaces Database System Utilities and Tools Centralized and Client-Server Architectures Classification of DBMSs 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 . entity record table and relationships among such groups Constraints specify some restrictions on valid data these constraints must be enforced at all times Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 2- 3 Copyright 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2-4 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 . generic insert delete update and user-defined operations . compute_student_gpa update_inventory 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. 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 Implementation representational data models Provide concepts that fall between the above two used by many commercial DBMS implementations . relational data models used in many commercial systems . Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 2- 5 Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 2- 6 1 Schemas versus Instances . Database Schema The description of a database. .