Database Systems: Design, Implementation, and Management - PDF

Database Systems: Design, Implementation, and Management Ninth Edition Chapter 2 Data Models Database Systems, 9th Edition 1  Objective...

Database Systems: Design, Implementation, and Management Ninth Edition Chapter 2 Data Models Database Systems, 9th Edition 1  Objectives In this chapter, you will learn: About data modeling and why data models are important About the basic data-modeling building blocks What business rules are and how they influence database design How the major data models evolved How data models can be classified by level of abstraction Database Systems, 9th Edition 2  Introduction Designers, programmers, and end users see data in different ways Different views of same data lead to designs that do not reflect organization’s operation Data modeling reduces complexities of database design Various degrees of data abstraction help reconcile varying views of same data Database Systems, 9th Edition 3  Data Modeling and Data Models Data models – Relatively simple representations of complex real-world data structures Often graphical Model: an abstraction of a real-world object or event – Useful in understanding complexities of the real-world environment Data modeling is iterative and progressive Database Systems, 9th Edition 4  The Importance of Data Models Facilitate interaction among the designer, the applications programmer, and the end user End users have different views and needs for data Data model organizes data for various users Data model is an abstraction Database Systems, 9th Edition 5  Data Model Basic Building Blocks Entity: anything about which data are to be collected and stored Attribute: a characteristic of an entity Relationship: describes an association among entities – One-to-many (1:M) relationship – Many-to-many (M:N or M:M) relationship – One-to-one (1:1) relationship Constraint: a restriction placed on the data Database Systems, 9th Edition 6  Business Rules Descriptions of policies, procedures, or principles within a specific organization – Apply to any organization that stores and uses data to generate information Description of operations to create/enforce actions within an organization’s environment – Must be in writing and kept up to date – Must be easy to understand and widely disseminated Describe characteristics of data as viewed by the company Database Systems, 9th Edition 7  Discovering Business Rules Sources of business rules: – Company managers – Policy makers – Department managers – Written documentation Procedures Standards Operations manuals – Direct interviews with end users Database Systems, 9th Edition 8 Discovering Business Rules (cont’d.) Standardize company’s view of data Communications tool between users and designers Allow designer to understand the nature, role, and scope of data Allow designer to understand business processes Allow designer to develop appropriate relationship participation rules and constraints Database Systems, 9th Edition 9  Translating Business Rules into Data Model Components Generally, nouns translate into entities Verbs translate into relationships among entities Relationships are bidirectional Two questions to identify the relationship type: – How many instances of B are related to one instance of A? – How many instances of A are related to one instance of B? Database Systems, 9th Edition 10  Naming Conventions Naming occurs during translation of business rules to data model components Names should make the object unique and distinguishable from other objects Names should also be descriptive of objects in the environment and be familiar to users Database Systems, 9th Edition 11  The Evolution of Data Models Database Systems, 9th Edition 12  The Hierarchical Model The hierarchical model was developed in the 1960s to manage large amounts of data for manufacturing projects Basic logical structure is represented by an upside-down “tree” Hierarchical structure contains levels or segments – Segment analogous to a record type – Set of one-to-many relationships between segments Database Systems, 9th Edition 13  The Network Model The network model was created to represent complex data relationships more effectively than the hierarchical model – Improves database performance – Imposes a database standard Resembles hierarchical model – However, record may have more than one parent Database Systems, 9th Edition 14  The Network Model (cont’d.) Collection of records in 1:M relationships Set composed of two record types: – Owner Equivalent to the hierarchical model’s parent – Member Equivalent to the hierarchical model’s child Database Systems, 9th Edition 15  The Network Model (cont’d.) Concepts still used today: – Schema Conceptual organization of entire database as viewed by the database administrator – Subschema Database portion “seen” by the application programs Database Systems, 9th Edition 16  The Network Model (cont’d.) Concepts still used today: (cont’d.) – Data management language (DML) Defines the environment in which data can be managed – Data definition language (DDL) Enables the administrator to define the schema components Database Systems, 9th Edition 17  The Network Model (cont’d.) Disadvantages of the network model: – Cumbersome – Lack of ad hoc query capability placed burden on programmers to generate code for reports – Structural change in the database could produce havoc in all application programs Database Systems, 9th Edition 18  The Relational Model Developed by E.F. Codd (IBM) in 1970 Table (relations) – Matrix consisting of row/column intersections – Each row in a relation is called a tuple Relational models were considered impractical in 1970 Model was conceptually simple at expense of computer overhead Database Systems, 9th Edition 19  The Relational Model (cont’d.) Relational data management system (RDBMS) – Performs same functions provided by hierarchical model – Hides complexity from the user Relational diagram – Representation of entities, attributes, and relationships Relational table stores collection of related entities Database Systems, 9th Edition 20 Database Systems, 9th Edition 21 Database Systems, 9th Edition 22  The Relational Model (cont’d.) SQL-based relational database application involves three parts: – User interface Allows end user to interact with the data – Set of tables stored in the database Each table is independent from another Rows in different tables are related based on common values in common attributes – SQL “engine” Executes all queries Database Systems, 9th Edition 23  The Entity Relationship Model Widely accepted standard for data modeling Introduced by Chen in 1976 Graphical representation of entities and their relationships in a database structure Entity relationship diagram (ERD) – Uses graphic representations to model database components – Entity is mapped to a relational table Database Systems, 9th Edition 24  The Entity Relationship Model (cont’d.) Entity instance (or occurrence) is row in table Entity set is collection of like entities Connectivity labels types of relationships Relationships are expressed using Chen notation – Relationships are represented by a diamond – Relationship name is written inside the diamond Crow’s Foot notation used as design standard in this book Database Systems, 9th Edition 25 Database Systems, 9th Edition 26  The Object-Oriented (OO) Model Data and relationships are contained in a single structure known as an object OODM (object-oriented data model) is the basis for OODBMS – Semantic data model An object: – Contains operations – Are self-contained: a basic building-block for autonomous structures – Is an abstraction of a real-world entity Database Systems, 9th Edition 27  The Object-Oriented (OO) Model (cont’d.) Attributes describe the properties of an object Objects that share similar characteristics are grouped in classes Classes are organized in a class hierarchy Inheritance: object inherits methods and attributes of parent class UML based on OO concepts that describe diagrams and symbols – Used to graphically model a system Database Systems, 9th Edition 28 Database Systems, 9th Edition 29  Newer Data Models: Object/Relational and XML Extended relational data model (ERDM) – Semantic data model developed in response to increasing complexity of applications – Includes many of OO model’s best features – Often described as an object/relational database management system (O/RDBMS) – Primarily geared to business applications Database Systems, 9th Edition 30  Newer Data Models: Object/Relational and XML (cont’d.) The Internet revolution created the potential to exchange critical business information In this environment, Extensible Markup Language (XML) emerged as the de facto standard Current databases support XML – XML: the standard protocol for data exchange among systems and Internet services Database Systems, 9th Edition 31  The Future of Data Models Hybrid DBMSs – Retain advantages of relational model – Provide object-oriented view of the underlying data SQL data services – Store data remotely without incurring expensive hardware, software, and personnel costs – Companies operate on a “pay-as-you-go” system Database Systems, 9th Edition 32 Database Systems, 9th Edition 33  Data Models: A Summary Common characteristics: – Conceptual simplicity with semantic completeness – Represent the real world as closely as possible – Real-world transformations must comply with consistency and integrity characteristics Each new data model capitalized on the shortcomings of previous models Some models better suited for some tasks Database Systems, 9th Edition 34 Database Systems, 9th Edition 35  Degrees of Data Abstraction Database designer starts with abstracted view, then adds details ANSI Standards Planning and Requirements Committee (SPARC) – Defined a framework for data modeling based on degrees of data abstraction (1970s): External Conceptual Internal Database Systems, 9th Edition 36  The External Model End users’ view of the data environment ER diagrams represent external views External schema: specific representation of an external view – Entities – Relationships – Processes – Constraints Database Systems, 9th Edition 37 Database Systems, 9th Edition 38  The External Model (cont’d.) Easy to identify specific data required to support each business unit’s operations Facilitates designer’s job by providing feedback about the model’s adequacy Ensures security constraints in database design Simplifies application program development Database Systems, 9th Edition 39 Database Systems, 9th Edition 40  The Conceptual Model Represents global view of the entire database All external views integrated into single global view: conceptual schema ER model most widely used ERD graphically represents the conceptual schema Database Systems, 9th Edition 41 Database Systems, 9th Edition 42  The Conceptual Model (cont’d.) Provides a relatively easily understood macro level view of data environment Independent of both software and hardware – Does not depend on the DBMS software used to implement the model – Does not depend on the hardware used in the implementation of the model – Changes in hardware or software do not affect database design at the conceptual level Database Systems, 9th Edition 43  The Internal Model Representation of the database as “seen” by the DBMS – Maps the conceptual model to the DBMS Internal schema depicts a specific representation of an internal model Depends on specific database software – Change in DBMS software requires internal model be changed Logical independence: change internal model without affecting conceptual model Database Systems, 9th Edition 44 Database Systems, 9th Edition 45  The Physical Model Operates at lowest level of abstraction – Describes the way data are saved on storage media such as disks or tapes Requires the definition of physical storage and data access methods Relational model aimed at logical level – Does not require physical-level details Physical independence: changes in physical model do not affect internal model Database Systems, 9th Edition 46 Database Systems, 9th Edition 47  Summary A data model is an abstraction of a complex real-world data environment Basic data modeling components: – Entities – Attributes – Relationships – Constraints Business rules identify and define basic modeling components Database Systems, 9th Edition 48  Summary (cont’d.) Hierarchical model – Set of one-to-many (1:M) relationships between a parent and its children segments Network data model – Uses sets to represent 1:M relationships between record types Relational model – Current database implementation standard – ER model is a tool for data modeling Complements relational model Database Systems, 9th Edition 49  Summary (cont’d.) Object-oriented data model: object is basic modeling structure Relational model adopted object-oriented extensions: extended relational data model (ERDM) OO data models depicted using UML Data-modeling requirements are a function of different data views and abstraction levels – Three abstraction levels: external, conceptual, internal Database Systems, 9th Edition 50