Chapter 7 Review

Indifferent condtions

In a decision table, a condition whose value does not affect which actions are taken for two or more rules.

Explain the convention for naming different levels of DFDs.

*Context* Single process is labeled *0* *Level-0* Each process has a number that ends in .0 (corresponding to the level number of the DFD) *Level-1* Processes labeled as sub processes of Process *n*.0 (i.e. Process 1.1, 1.2, 2.1, 2.2 and so on) *Level-2* Processes labeled as further sub processes of Process *n*.0 (i.e. Process 4.3.1, 4.3.2)

Why do analysts draw multiple sets of DFDs?

*Iterative Development* - Analyst should expect to redraw a diagram several times before reaching the closest approximation to the system being modeled

What is a DFD? Why do systems analysts use DFDs?

A DFD (data flow diagram) is a picture of the movement of data between external entities and the processes and data stores within a system System Analysts use DFDs to organize the abundance of information gathered during the requirements determination phase into a meaningful representation of the information system that currently exists and of the requirements desired in a replacement system.

Level-n diagram

A DFD that is the result of n nested decompositions from a process on a level-0 diagram.

Level-0 diagram

A DFD that represents a system's major processes, data flows, and data stores at a high level of detail.

Decision table

A matrix representation of the logic of a decision, which specifies the possible conditions for the decision and the resulting actions.

Data Flow Diagram (DFD)

A picture of the movement of data between external entities and the processes and data stores within a system.

Functional decomposition

An iterative process of breaking the description of a system down into finer and finer detail, which creates a set of charts in which one process on a given chart is explained in greater detail on another chart.

Context diagram

An overview of an organizational system that shows the system boundaries, external entities that interact with the system, and the major information flows between the entities and the system.

What unique rules apply to drawing context diagrams?

Contains *only one process*, representing the entire system (this process is given the number *0*) All *external entities*, as well as major data flows to and from them are shown Does *not contain any Data stores* Provides *birds-eye view* of data movement in the system and the *broadest possible conceptualization* of the system Helps systems analyst grasp *basic data movement*, but its general nature limits its usefulness

How can DFDs be used as analysis tools?

DFDs help determine the completeness of a system model and a models internal consistency, as a way to determine when system events occur

Data store

Data at rest, which may take the form of many different physical representations.

Explain the rules for drawing good DFDs.

Data flow - arrow Source/sink - square Data store - rectangle that is missing its right vertical side Process - rectangle with rounded corners

What is decomposition? What is balancing? How can you determine if DFDs are not balanced?

Decomposition is an iterative process of breaking a system description down into finer and finer detail. Balancing is the conservation of inputs and outputs to a DFD process when that process is decomposed to a lower level. Determine if it is balanced by observing whether or not a process that appears in a level-n diagram has the same inputs and outputs when decomposed for a lower-level diagram

How do you decide if a system component should be represented as a source/sink or as a process?

Sources/sinks are external to the system. Sources/sinks are the origin and/or destination of data Sources/sinks may consist of: • Another organization or organization unit that sends data to or receives data from the system you are analyzing • A person inside or outside the business unit supported by the system you are analyzing who interacts with the system • Another information system with which they system you are analyzing exchanges information A process is the work or actions performed on data so that they are transformed, stored, or distributed

What are the steps in creating a decision table? How do you reduce the size and complexity of a decision table?

Steps: Name the condition and the values that each condition can assume. Name all possible actions that can occur. List all possible rules. Define the actions for each rule. Simplify the table. *Simplify a decision table by:* removing any rules with impossible actions; use separate, linked decision tables, or use numbers that indicate sequence rather than X's where rules and action stubs intersect; identifying indifferent conditions

Balancing

The conservation of inputs and outputs to a DFD process when that process is decomposed to a lower level.

DFD completeness

The extent to which all necessary components of a DFD have been included and fully described

DFD consistency

The extent to which information contained on one level of a set of nested DFDs is also included on other levels.

Primitive DFD

The lowest level of decomposition for a DFD.

Source/sink

The origin and/or destination of data; sometimes referred to as external entities.

Action stubs

The part of a decision table that lists the actions that result for a given set of conditions.

Condition stubs

The part of a decision table that lists the conditions relevant to the decision.

Rules

The part of a decision table that specifies which actions are to be followed for a given set of conditions.

Gap analysis

The process of discovering discrepancies between two or more sets of DFDs or discrepancies within a single DFD.

Process

The work or actions performed on data so that they are transformed, stored or distributed.

Explain the guidelines for deciding when to stop decomposing DFDs.

When each *process* has been reduced to a single decision, calculation or database operation When each *data store* represents data about a single entity - e.g. customer, employee, etc. When the *system user* does not care to see any more detail When every *data flow* does not need to be split further to show that data are handled in various ways When you believe that you have shown each business form or transaction, online display and report as a single data flow When you believe that there is a separate process for each choice on all lowest-level menu options

What is the formula that is used to calculate the number of rules a decision table must cover?

number of values for each condition * number of values for every other condition