Chapter 1 Database Systems: Architecture and Components

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Chapter 1 – Database Systems: Architecture and Components

Chapter 1 Objectives

After completing this chapter, the student will understand:

• The difference between data, metadata, and information and highlight how metadata serves as the lens by which data can become information • How data management is a discipline that focuses on the proper acquisition, storage, maintenance, and retrieval of data • The characteristics of file-processing systems and their limitations • How the ANSI/SPARC Three-Schema Architecture constitutes the solution to the problems plaguing file processing systems • What constitutes a database, a database management system, and a database • The difference between a model and a data model • The role of data models in database design • The role of the three data models (conceptual, logical, and physical) in the database design life cycle portrayed in Figure 1.7

Chapter 1 Overview

This chapter begins with an introduction to the rudimentary concepts of data and how information emerges from data when viewed through the lens of metadata. Next, the discussion addresses data management, contrasting file-processing systems with database systems. This is followed by brief examples of desktop, workgroup, and enterprise databases. The chapter then presents a framework for database design in Figure 1.7 that describes the conceptual, logical, and physical tiers of data modeling and their roles in the database design life cycle. This framework serves as the roadmap to guide the reader through the remainder of the book. Finally, an example walks one through the cradle to grave life cycle of data modeling and database design in a nutshell.

(Data Modeling and Database Design 2e Narayan Umanath, Richard Scamell) (Solution Manual all Chapters) 1 / 4

Data Modeling and Database Design 1-2 Chapter 1 Key Terms

Data Unorganized facts about things, events, activities, and transactions.Information Data that has been organized into a specific context such that it has value to its recipient.Metadata A lens through which data takes on specific meaning and yields information.Data element The smallest unit of data.Record type A group of related data elements treated as a unit.Record A set of values for the data elements constituting a record type.File A collection of records.Data Set Another term for a file.Sequential access An access approach where in order to get to the nth record in a data set it is necessary to pass through the previous n-1 records in the data set.Direct access An access approach where it is possible to get to the nth record in a data set without having to pass through the previous n-1 records in the data set.File-processing system The predecessor of a database system where records were stored in separate non-integrated files.Data integrity Ensures that data is correct, consistent, complete, and current.ANSI/SPARC three-schema architecture A collection of three separate schemas or views

for describing data in a database: (a) external

schema (or application view), (b) conceptual schema (or logical view) and (c) internal schema (or physical view).Conceptual schema Represents the global conceptual view of the structure of the entire database for the community of users. It is independent of any particular data structure or data representation.External schema Consists of a number of different user views or subschemas, each describing portions of the database of interest to a par ticular user or group of users. The external schema describes the data corresponding to part of the conceptual schema as seen by one or more users or programs. 2 / 4

Data Modeling and Database Design 1-3

Internal schema Describes the physical structure of the stored data and the mechanism used to implement the access strategy. As opposed to the conceptual schema and external schema, which are technology- independent, the internal schema is technology- dependent.Data independence The ability to modify a schema definition in one level without affecting a schema definition in a higher level. For example, the conceptual schema insulates user views in the external schema from changes in the physical storage structure of the data in the internal schema.Physical data independence The ability to modify the internal schema without causing the application program in the external schema to be rewritten.Logical data independence The immunity of a user view from changes in the other user views.Database A self-describing collection of integrated files consisting of (1) users’ data, (2) metadata, and (3) overhead data.Database management system A collection of general-purpose software that facilitates the processes of defining, constructing, and manipulating a database for various applications.Distributed database A collection of multiple logically interrelated databases that may be geographically dispersed over a computer network.Distributed database management system Software that manages a distributed database while rendering the geographical distribution of the data transparent to the user community.Data warehouse A collection of data designed to support management decision making. A data warehouse contains a wide variety o f data that present a coherent picture of business conditions at a single point in time.Data definition language (DDL) The component of a database management system used to create the structure of database objects such as tables, views, assertions, domains, schemas, etc.Data control language (DCL) The component of a database management system used to control user access, facilitate backup and recovery from failures, and insure that users access only the data they are authorized to use. 3 / 4

Data Modeling and Database Design 1-4

Data manipulation language (DML) The component of a database management system product that facilitates the retrieval, insertion, deletion, and modification of data in a database.Data dictionary The component of a database system that stores metadata that provides such information as the definitions of data items and their relationships, authorizations, and usage statistics.Data repository A collection of metadata about data models and application program interfaces.Data model A representation of a real-world phenomenon that makes use of descriptors.Universe of interest The aspect of the real world represented by the database.Requirements specification The initial step in the database design process where existing documents and systems are reviewed and prospective users are interviewed in an effort to identify the objectives to be supported by the database system.Business rules User-specified restrictions on the organization’s activities (business processes) that must be reflected in the database or database applications.Business rule (from Chapter 2) A short statement of a specific condition or procedure relevant to the universe of interest being modeled expressed in a precise, unambiguous manner.Conceptual data modeling Involves describing the structure of the data to be stored in the database without specifying how it will be physically stored.Logical data modeling Involves refining the conceptual data model to (a) the point where it is more compatible with the technology intended for implementation and (b) eliminate data redundancy problems.Physical data modeling Involves transforming the logical data model into a form that can be implemented by some DBMS product.

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