Relational Database and Data Modeling Lecture 10 (Chapter 4)

Introduction This lecture explains what a database is and how it differs from a file-oriented system. It describes the structure of a relational database system & the basic steps involved in designing a database. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Databases For many years, companies created new files and programs each time an information need arose. This proliferation of master files created problems: Often the same data was stored in two or more separate files. The specific data values stored in the different files were not always consistent. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Databases The database approach views data as an organizational resource that should be used by, and managed for, the entire organization, not just the originating department or function. Its focus is data integration and data sharing. Integration is achieved by combining master files into larger pools of data that can be accessed by many application programs. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Types of Files Two basic types of files are used to store data: The master file, which is conceptually similar to a ledger in a manual system. The transaction file, which is conceptually similar to a journal in a manual system. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

File-Oriented Approach Application program #1 Item A Item B Item C File # 2 Application program #2 Item B Item D Item E ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Database Approach Application Database program #1 Item A Item B Item C Item D Item E Application program #2 Database management system Application program #3 ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Database Approach versus File-Oriented Approach Minimum data redundancy Fewer data inconsistencies Standardized data format No duplicated processing or storage Allows cross-functional data analyses Central data management / data security Lower cost ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Databases Database management system (DBMS) is the program that manages and controls access to the database. Database system is the combination of the database, the DBMS, and the application program that uses the database. Database administrator (DBA) is the person responsible for the database. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Relational Databases A data model is an abstract representation of the contents of a database. The relational data model represents everything in the database as being stored in the form of tables. Technically, these tables are called relations. Each row in a relation, called a tuple, contains data about a specific occurrence of the type of entity represented by that table. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Logical & Physical Views of Data A major advantage of database systems over file-oriented systems is that the database systems separate the logical and physical view of data: Logical view: It is how the user or programmer conceptually organizes and understands the data. Physical view: It refers to how and where the data are physically arranged and stored on disk, tape, CD-ROM, or other media. The DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Schemas What are schemas? A schema describes the logical structure of a database. There are three levels of schemas: Conceptual-level schema External-level schema Internal-level schema ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Schemas Schema Levels: Conceptual External Internal The conceptual-level schema is an organization-wide view of the entire database. The external-level schema consists of a set of individual user views of portions of the database, also referred to as a subschema. The internal-level schema provides a low-level view of the database. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

The Data Dictionary What is a data dictionary? It contains information about the structure of the database. For each data element stored in the database, such as the customer number, there is a corresponding record in the data dictionary describing it. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

The Data Dictionary Inputs to the data dictionary: The data dictionary is often one of the first applications of a newly implemented database system. Inputs to the data dictionary: records of any new or deleted data elements changes in names, descriptions, or uses of existing data elements Outputs of the data dictionary: reports useful to programmers, database designers, and users of the information system ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

DBMS Languages Every DBMS must provide a means of performing the three basic functions: Creating the database Changing the database Querying the database The sets of commands used to perform these functions are referred to as the data definition, data manipulation, and data query languages. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

DBMS Languages Data definition language (DDL): build the data dictionary. initialize or create the database. describe the logical views for each individual user or programmer. specify any limitations or constraints on security imposed on database record or fields. Data manipulation language (DML): Data maintenance (updating / inserting / deleting) Data query language (DQL): Interrogate the database (retrieves / sorts / orders and and presents subsets of the database in response to user queries) ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Basic Requirements of the Relational Data Model Primary keys must be unique. Every foreign key must either be null or have a value corresponding to the value of a primary key in another relation. Each column in a table must describe a characteristic of the object identified by the primary key. Each column in a row must be single-valued. The value in every row of a specific column must be of the same data type. Neither column order nor row order is significant. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Database Design Objectives Completeness Relevance Accessibility Up-to-dateness flexibility Efficiency Cost-effectiveness Integrity Security ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Approaches to Database Design Normalization Starts with the assumption that all data is initially stored in a large non-normalized table. This table is then decomposed using a set of normalization rules to create a set of tables in the Third Normal Form. Semantic Data Modeling The database designer uses his/her knowledge about the business structure to create a set of relational tables. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Designing and Implementing a Database System Six basic steps involved in designing and implementing a database system: Initial planning to determine the need for and feasibility of developing a new system. Identifying user needs. Developing the contextual-, external-and internal-level schemas. Translating the internal-level schema into the actual database structures that will be implemented in the new system. Transferring all data from the existing system to the new database. Using and maintaining the new system. ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

The REA Data Model Data modeling is the process of defining a database so that it represents all aspects of the organization, including its interactions with the external environment. The REA data model is a conceptual modeling tool specifically designed to provide structure for designing AIS databases. REA data model provides structure in two ways: By identifying what entities should be included in the AIS database By prescribing how to structure relationships among the entities in the AIS database ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

End of Lecture 10 ©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart