【考试不慌】ISS615 Database Mgt学习笔记(1) The Database Environment

Basic Concepts and definitions

Data: “a stored representation of objects and events that have meaning and importance in the user’s environment.”

The database approach

Data Model

Data models capture the nature of and relationships among data and are used at different levels of abstraction as a database is conceptualized and designed.

Entities

Customers and orders are objects about which a business maintains information. They are referred to as “entities.” An entity is like a noun in that it describes a person, a place, an object, an event, or a concept in the business environment for which information must be recorded and retained

Relationships

A well-structured database establishes the relationships between entities that exist in organizational data so that desired information can be retrieved. Most relationships are one-to-many (1:M) or many-to-many (M:N).

A customer can place (the Places relationship) more than one order with a company. However, each order is usually associated with (the Is Placed By relationship) a particular customer.

Relational databases

establish the relationships between entities by means of common fields included in a file, called a relation. Relational databases use the identification number to establish the relationship between customer and order.

A database management system (DBMS)

is a software system that enables the use of a database approach. The primary purpose of a DBMS is to provide a systematic method of creating, updating, storing, and retrieving the data stored in a database. It enables end users and application programmers to share data, and it enables data to be shared among multiple applications rather than propagated and stored in new files for every new application (Mullins, 2002).

The database development process

Enterprise data modeling

The first step in database development, in which the scope and general contents of organizational databases are specified.

Database development activities during the systems development life cycle (SDLC)

Logical schema:

The representation of a database for a particular data management technology.

Physical schema:

Specifications for how data from a logical schema are stored in a computer’s secondary memory by a database management system.

There is one physical schema for each logical schema.

Physical database design requires knowledge of the specific DBMS that will be used to implement the database. In physical database design and definition, an analyst decides on the organization of physical records, the choice of file organizations, the use of indexes, and so on. To do this, a database designer needs to outline the programs to process transactions and to generate anticipated management information and decision-support reports.

The goal is to design a database that will efficiently and securely handle all data processing against it. Thus, physical database design is done in close coordination with the design of all other aspects of the physical information system: programs, computer hardware, operating systems, and data communications networks.

Implementation

Database Implementation In database implementation, a designer writes, tests, and installs the programs/scripts that access, create, or modify the database. The designer might do this using standard programming languages (e.g., Java, C#, or Visual Basic.NET) or in special database processing languages (e.g., SQL) or use special-purpose nonprocedural languages to produce stylized reports and displays, possibly including graphs.

Maintenance—Database Maintenance 

This is typically the longest step of database development, because it lasts throughout the life of the database and its associated applications. Each time the database evolves, view it as an abbreviated database development process in which conceptual data modeling, logical and physical database design, and database implementation occur to deal with proposed changes.

Alternative information systems (IS) development approaches

One of the most popular RAD methods is prototyping, which is an iterative process of systems development in which requirements are converted to a working system that is continually revised through close work between analysts and users.

three-schema architecture—external, conceptual, and internal schemas

1. External schema This is the view (or views) of managers and other employees who are the database users. As shown in Figure 1-9, the external schema can be represented as a combination of the enterprise data model (a top-down view) and a collection of detailed (or bottom-up) user views.

2. Conceptual schema This schema combines the different external views into a single, coherent, and comprehensive definition of the enterprise’s data. The conceptual schema represents the view of the data architect or data administrator.

3. Internal schema As shown in Figure 1-9, an internal schema today really consists of two separate schemas: a logical schema and a physical schema. The logical schema is the representation of data for a type of data management technology (e.g., relational). The physical schema describes how data are to be represented and stored in secondary storage using a particular DBMS (e.g., Oracle).

Database Applications

Enterprise Applications

An enterprise (that’s small “e,” not capital “E,” as in Starship) application/database is one whose scope is the entire organization or enterprise (or, at least, many different departments)

Enterprise resource planning (ERP)

A business management system that integrates all functions of the enterprise, such as manufacturing, sales, finance, marketing, inventory, accounting, and human resources. ERP systems are software applications that provide the data necessary for the enterprise to examine and manage its activities. Data warehouse An integrated decision support database whose content is derived from the various operational databases.

Data warehouses

collect content from the various operational databases, including personal, workgroup, department, and ERP databases.

Designing the Database