Database Systems: Design, Implementation, and Management PDF

Database Systems: Design, Implementation, and Management Tenth Edition Chapter 2 Data Models Database Systems, 10th Edition 1  Obje...

Database Systems: Design, Implementation, and Management Tenth Edition Chapter 2 Data Models Database Systems, 10th 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 Database Systems, 10th Edition 2  Objectives (cont’d.) About emerging alternative data models and the need they fulfill How data models can be classified by their level of abstraction Database Systems, 10th Edition 3  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, 10th Edition 4  Data Modeling and Data Models Data modeling, the first step in designing a database, It refers to the process of creating a specific data model for a determined problem domain. A problem domain is a clearly defined area within the real-world environment, with well- defined scope and boundaries, that will be systematically addressed. Database Systems, 10th Edition 5  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 Within the database environment, a data model represents data structures and their characteristics, relations, constraints, transformations, and other constructs with the purpose of supporting a specific problem domain.. – A data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently. Database Systems, 10th Edition 6  Data Modeling and Data Models When done properly, the final data model effectively is a “blueprint” with all the instructions to build a database that will meet all end-user requirements. This blueprint is narrative and graphical in nature, meaning that it contains both text descriptions in plain, unambiguous language and clear, useful diagrams depicting the main data elements. An implementation-ready data model should contain at least the following components: – A description of the data structure that will store the end-user data. – A set of enforceable rules to guarantee the integrity of the data. – A data manipulation methodology to support the real-world data transformations. Database Systems, 10th Edition 7  The Importance of Data Models Facilitate interaction among the designer, the applications programmer, and the end user. – “A well-developed data model can even foster improved understanding of the organization for which the database design is developed. – data models are a communication tool. – Data constitute the most basic information units employed by a system. Applications are created to manage data and to help transform data into information, but data are viewed in different ways by different people. End users have different views and needs for data Data model organizes data for various users Data model is an abstraction – Cannot draw required data out of the data model Database Systems, 10th Edition 8  Data Model Basic Building Blocks The basic building blocks of all data models are entities, attributes, relationships, and constraints.” Entity: anything (person, place, thing, or event) about which data are to be collected and stored An entity represents a particular type of object in the real world, which means an entity is “distinguishable”— that is, each entity occurrence is unique and distinct. Entities may be physical objects, or abstractions, Attribute: a characteristic of an entity. – Attributes are the equivalent of fields in file systems.” Database Systems, 10th Edition 9  Data Model Basic Building Blocks Relationship: describes an association among entities – One-to-many (1:M, 1..*) relationship – Many-to-many (M:N or M:M,M..N) relationship – One-to-one (1:1,1..1) relationship One-to-many (1:M or 1..*) relationship. – A painter creates many different paintings, but each is painted by only one painter. – Similarly, a customer (the “one”) may generate many invoices, but each invoice (the “many”) is generated by only a single customer. ” Database Systems, 10th Edition 10  Data Model Basic Building Blocks Many-to-many (M:N or *..*) relationship. – An employee may learn many job skills, and each job skill may be learned by many employees. – Similarly, a student can take many classes and each class can be taken by many students, thus yielding the M:N label for the relationship expressed by “STUDENT takes CLASS. One-to-one (1:1 or 1..1) relationship. – A retail company’s management structure may require that each of its stores be managed by a single employee. In turn, each store manager, who is an employee, manages only a single store. Database Systems, 10th Edition 11  Data Model Basic Building Blocks Each relationship in both directions; that is, relationships are bidirectional Database Systems, 10th Edition 12  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, 10th Edition 13  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, 10th Edition 14 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, 10th Edition 15  Translating Business Rules into Data Model Components 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, 10th Edition 16  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 Proper naming: – Facilitates communication between parties – Promotes self-documentation Database Systems, 10th Edition 17  The Evolution of Data Models Database Systems, 10th Edition 18  Hierarchical and Network Models The hierarchical model – Developed in the 1960s to manage large amounts of data for manufacturing projects – Basic logical structure is represented by an upside-down “tree” – Structure contains levels or segments Database Systems, 10th Edition 19  Hierarchical and Network Models (cont’d.) Network model – Created to represent complex data relationships more effectively than the hierarchical model – Improves database performance – Imposes a database standard – Resembles hierarchical model Record may have more than one parent Database Systems, 10th Edition 20  Hierarchical and Network Models (cont’d.) – Collection of records in 1:M relationships – Set composed of two record types: Owner Member Network model 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, 10th Edition 21  Hierarchical and Network Models (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, 10th Edition 22  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, 10th Edition 23  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, 10th Edition 24 Database Systems, 10th Edition 25 Database Systems, 10th Edition 26  The Relational Model (cont’d.) SQL-based relational database application involves three parts: – End-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, 10th Edition 27  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, 10th Edition 28  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, 10th Edition 29 Database Systems, 10th Edition 30  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, 10th Edition 31  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, 10th Edition 32 Database Systems, 10th Edition 33  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, 10th Edition 34  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, 10th Edition 35 Emerging Data Models: Big Data and NoSQL Big Data – Find new and better ways to manage large amounts of Web-generated data and derive business insight from it – Simultaneously provides high performance and scalability at a reasonable cost – Relational approach does not always match the needs of organizations with Big Data challenges Database Systems, 10th Edition 36 Emerging Data Models: Big Data and NoSQL (cont’d.) NoSQL databases – Not based on the relational model, hence the name NoSQL – Supports distributed database architectures – Provides high scalability, high availability, and fault tolerance – Supports very large amounts of sparse data – Geared toward performance rather than transaction consistency Database Systems, 10th Edition 37 Emerging Data Models: Big Data and NoSQL (cont’d.) Key-value data model – Two data elements: key and value Every key has a corresponding value or set of values Sparse data – Number of attributes is very large – Number of actual data instances is low Eventual consistency – Updates will propagate through system; eventually all data copies will be consistent Database Systems, 10th Edition 38 Database Systems, 10th Edition 39  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, 10th Edition 40 Database Systems, 10th Edition 41  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, 10th Edition 42  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, 10th Edition 43 Database Systems, 10th Edition 44  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, 10th Edition 45  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, 10th Edition 46 Database Systems, 10th Edition 47  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, 10th Edition 48  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, 10th Edition 49 Database Systems, 10th Edition 50  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, 10th Edition 51 Database Systems, 10th Edition 52  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, 10th Edition 53  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, 10th Edition 54  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, and internal Database Systems, 10th Edition 55