MIS Exam #2 Part Two

Business Rules (275)

Specifications that preserve the integrity of the logical data model.

What role do "business rules" play in data modeling?

Specifications that preserve the integrity of the logical data model. Conceptual data modeling is a step-by-step process for documenting information re- quirements, and it is concerned with both the structure of data and with rules about the integrity of those data.

What is a "triggering operation" and what purpose does it serve? Illustrate with an example. (278)

a triggering operation is an assertion or rule that governs the validity of data manipulation operations such as insert, update, and delete; also called a trigger. 1. User rule: A concise statement of the business rule to be enforced by the trigger- ing operation. 2. Event: The data manipulation operation (insert, delete, or update) that initiates the operation. 3. Entity name: The name of the entity being accessed and/or modified. 4. Condition: The condition that causes the operation to be triggered. 5. Action: The action taken when the operation is triggered.

Do ER diagrams replace DFDs? Or do ER diagrams supplement DFDs? Please explain.**

Yes it can replace DFDs, because of..

What is an "associative entity"?

An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity Instances; also called a gerund.

Why is it useful to provide "domain" definitions for data? Illustrate with an example.

Because they specific some (or all) of the following characteristics of attributes: data, length, format, range, allowable values, meaning, uniqueness, and null support (whether an attribute value may or may not be null.

What type of information relating to data modeling is stored in the project dictionary? Illustrate with examples.

The other deliverable from conceptual data modeling is a full set of entries about data objects that will be stored in the project dictionary, repository, or data modeling software. The repository is the mechanism that links the data, processes, and logic models of an information system. For example, there are explicit links between a data model and a DFD. Some important links are explained briefly here. Data elements included in data flows also appear in the data model,and vice versa. You must include in the data model any raw data captured and retained in a data store, and a data model can include only data that have been captured or that have been computed from captured data. Because a data model is a general business picture of data, both manual and automated data stores will be included. Each data store in a process model must relate to business objects (what we will call data entities) represented in the data model. For example, in Figure 7-5, the Inventory File data store must correspond to one or several data objects on a data model.

Suppose that an analyst is working on a systems project and has started off by preparing a set of DFDs and the associated project dictionary entries. Next, suppose that the analyst prepares the ER data model for the project. Is there any information regarding the DFDs in the project dictionary (e.g., information about data flows, process logic, etc.) that could be used to help with the data modeling process (e.g., identification of entity attributes)? If so, what information might be useful and how could it be used?

The work of all team members is coordinated and shared through the project dictionary or repository. This repository is often maintained by a common Computer- Aided Software Engineering (CASE) or data modeling software tool, but some orga- nizations still use spreadsheets and other types of files to store data descriptions and other important information. No matter how the information is stored, it is essential that the process, logic, and data model descriptions of a system are consistent and complete because each describes different, but complementary, views of the same information system. For example, the names of data stores on the primitive- level DFDs often correspond to the names of data entities in E-R diagrams, and the data elements associated with data flows on DFDs must be accounted for by attributes of entities and relationships in E-R diagrams.

Provide an example of a situation when it would it make sense for a relationship to have an attribute(s).

Unary, Binary, Ternary