Database Design | What is the relationship between a database and an information system, and how does this relationship have a bearing on database design?

Chapter 9

Database Design

Discussion Focus

What is the relationship between a database and an information system, and how does this

relationship have a bearing on database design?

An information system performs three sets of services:

· It provides for data collection, storage, and retrieval.

· It facilitates the transformation of data into information.

· It provides the tools and conditions to manage both data and information.

Basically, a database is a fact (data) repository that serves an information system. If the database is

designed poorly, one can hardly expect that the data/information transformation will be successful, nor

is it reasonable to expect efficient and capable management of data and information.

The transformation of data into information is accomplished through application programs. It is

impossible to produce good information from poor data; and, no matter how sophisticated the

application programs are, it is impossible to use good application programs to overcome the effects of

bad database design. In short: Good database design is the foundation of a successful information

system.

Database design must yield a database that:

· Does not fall prey to uncontrolled data duplication, thus preventing data anomalies and the

attendant lack of data integrity.

· Is efficient in its provision of data access.

· Serves the needs of the information system.

The last point deserves emphasis: even the best-designed database lacks value if it fails to meet

information system objectives. In short, good database designers must pay close attention to the

information system requirements.

Systems design and database design are usually tightly intertwined and are often performed in parallel.

Therefore, database and systems designers must cooperate and coordinate to yield the best possible

information system.

What is the relationship between the SDLC and the DBLC?

The SDLC traces the history (life cycle) of an information system. The DBLC traces the history (life

cycle) of a database system. Since we know that the database serves the information system, it is not

surprising that the two life cycles conform to the same basic phases.

Suggestion: Use Figure 9.8 as the basis for a discussion of the parallel activities.

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Chapter 9 Database Design

What basic database design strategies exist, and how are such strategies executed?

Suggestion: Use Figure 9.14 as the basis for this discussion.

There are two basic approaches to database design: top-down and bottom-up.

Top-down design begins by identifying the different entity types and the definition of each entity's

attributes. In other words, top-down design:

· starts by defining the required data sets and then

· defines the data elements for each of those data sets.

Bottom-up design:

· first defines the required attributes and then

· groups the attributes to form entities.

Although the two methodologies tend to be complementary, database designers who deal with small

databases with relatively few entities, attributes, and transactions tend to emphasize the bottom-up

approach. Database designers who deal with large, complex databases usually find that a primarily

top-down design approach is more appropriate.

In spite of the frequent arguments concerning the best design approach, perhaps the top-down vs.

bottom-up distinction is quite artificial. The text's note is worth repeating:

NOTE

Even if a generally top-down approach is selected, the normalization process that revises

existing table structures is (inevitably) a bottom-up technique. E-R models constitute a topdown process even if the selection of attributes and entities may be described as bottom-up.

Since both the E-R model and normalization techniques form the basis for most designs, the

top-down vs. bottom-up debate may be based on a distinction without a difference.

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Chapter 9 Database Design

Answers to Review Questions

1. What is an information system? What is its purpose?

An information system is a system that

· provides the conditions for data collection, storage, and retrieval

· facilitates the transformation of data into information

· provides management of both data and information.

An information system is composed of hardware, software (DBMS and applications), the

database(s), procedures, and people.

Good decisions are generally based on good information. Ultimately, the purpose of an information

system is to facilitate good decision making by making relevant and timely information available to

the decision makers.

2. How do systems analysis and systems development fit into a discussion about information

systems?

Both systems analysis and systems development constitute part of the Systems Development Life

Cycle, or SDLC. Systems analysis, phase II of the SDLC, establishes the need for and the extent of

an information system by

· Establishing end-user requirements.

· Evaluating the existing system.

· Developing a logical systems design.

Systems development, based on the detailed systems design found in phase III of the SDLC, yields

the information system. The detailed system specifications are established during the systems

design phase, in which the designer completes the design of all required system processes.

3. What does the acronym SDLC mean, and what does an SDLC portray?

SDLC is the acronym that is used to label the System Development Life Cycle. The SDLC traces

the history of a information system from its inception to its obsolescence. The SDLC is composed