Chapter 5 - Process Modeling

Question 1

What is a process model? Give some examples.

Answer 1

A process model is a graphical model that is used to further clarify the requirements definition and use cases, showing how a system should operate. Process models can illustrate either the as-is or to-be systems. 
Examples of a process model would be:
- Data Flow Diagrams
- Logical Process Models
- Physical Models

Question 2

What are the four symbols used in data flow diagrams?

Answer 2

The four data flow diagram symbols are processes, data flows, data stores, and external entities.

Question 3

What is a process?

Answer 3

A process is an activity or function that is performed for some specific business reason. Processes can be manual or automated.

Question 4

How are processes represented and named in a data flow diagram?

Answer 4

In a data flow diagram, a process should always begin with a verb and end with a noun. They should also have a number assigned to them. The symbol of a process is a rounded rectangle with a shaded upper region, where the process number belongs. The unshaded area should contain the process name.

Question 5

How are data flows represented and named in a data flow diagram?

Answer 5

Data flows are represented by arrows connecting either processes, data stores, or external entities. They are named after nouns.

Question 6

How are data stores represented and named in a data flow diagram?

Answer 6

Data stores are represented by a thin rectangle with a small shaded square filling the first 1/5th. Inside this square, the data flow number (D1, D3, etc) is placed. Following it, the data store name is placed.
Every data store should have a noun-based name, a number, a description, and one or more input and output data flows.

Question 7

How are external entities represented in a data flow diagram?

Answer 7

External entities are represented by large rectangles in a data flow diagram, and their names are based off of nouns.

Question 8

What is data flow diagramming?

Answer 8

Data flow diagramming is the technique of diagramming business processes and the data that pass among them.

Question 9

What is a logical process model?

Answer 9

A logical process model is a model that describes processes, without worrying about how they are conducted (in regards to the steps behind the process, if it’s manual or computerized, etc).

Question 10

Why is it that one DFD cannot contain an entirety of a business’s processes? How is this gotten around?

Answer 10

Business processes are far too complex to be explained in any one DFD. This is gotten around by using decomposition of business processes into multiple DFDs, with lower level DFDs representing a more granular level of detail.

Question 11

What is a context diagram?

Answer 11

A context diagram is the very highest level of DFD, and the first DFD in any business process. It is called a context diagram because it shows the entire system in context with its environment, representing the overall business process as one process, and showing the data flows in and out of that process to external entities.

Question 12

What is a Level 0 DFD?

Answer 12

A level 0 data flow diagram is a high-level DFD that shows all the major high-level processes of a system, and how they are all interrelated, with each other and with the data stores, data flows, and external entities. A process model will only have one level 0 DFD.

Question 13

What is balancing in regards to DFDs?

Answer 13

Balancing, in regards to data flow diagrams, is the act of ensuring that all information presented at one level of data flow diagram is represented accurately at the next levels of DFD.

Question 14

What is a level 1 DFD? How is it created?

Answer 14

A level 1 data flow diagram is a subset of the level 0 DFD, decomposed from one of the processes shown there.

It is worth knowing that the set of children together are identical to their parent DFD. In addition, there are as many level 1 DFDs as there are processes in the level 0 DFD.

Question 15

What is a level 2 DFD? How is it created?

Answer 15

A level 2 data flow diagram is a subset of the level 1 DFD, decomposed from one of the processes shown there.

It is worth knowing that the set of children together are identical to their parent DFD.

Question 16

What are alternative data flows, and how are they represented in a data flow diagram?

Answer 16

Alternative data flows are a result when a process can produce different data flows in differing circumstances. They are represented in a DFD by both being shown, with their differences explained in the process description.

Question 17

How are data flow diagrams created? What are the steps needed to build a DFD?

Answer 17

Data flow diagrams are created from consulting use cases and requirements definition. The steps are:

1. Build the context diagram.
2. Create DFD fragments from each use case.
3. Organize the DFD fragments in the level 0 DFD
4. Develop level 1 DFDs based on the steps in each use case. Decompose as necessary
5. Validate DFDs.

Question 18

How is a context diagram created?

Answer 18

A context diagram is a simple thing to create. The system itself is represented by a process symbol, labeled as “0” and either the process name or system. All inputs and outputs listed on the use cases become data flows, and all external entities are added in. Data stores are NOT shown.

Question 19

What is a DFD fragment?

Answer 19

A data flow diagram fragment is one piece of a data flow diagram that will eventually be combined with other fragments to form a full DFD. Each use case becomes a fragment, using a name, ID number, and its major inputs and outputs. Major steps aren’t used at this point.

Question 20

How is a level 0 DFD created?

Answer 20

A level 0 DFD is built by combining the data flow diagram fragments together into one diagram. There are no formal layout rules for a level 0 DFD, save to attempt to prevent crossed lines whenever possible.

Question 21

How is a level 1 DFD created?

Answer 21

A level 1 DFD is created by decomposing each process/DFD fragment within the level 0 DFD. Each major step within the corresponding use case becomes a process within the level 1 DFD. Data stores are included at level 1, and are modeled from the inputs and outputs in the corresponding use case.

Question 22

What are the rules of thumb for creating a rule of thumb?

Answer 22

Rules of thumb:
There should be at least three and no more than seven processes per DFD. Processes need to be decomposed until you can provide a detailed description of the process with no more than one page of description.

Question 23

What are syntax errors in a data flow diagram?

Answer 23

Syntax errors in a data flow diagram are grammatical errors, things that violate the rules of DFD language. Things like having a data flow between two entities between a data store and an entity, without having a process to do it, or having a double-headed data flow.

Question 24

What is a “black hole” in a DFD?

Answer 24

A black hole in a DFD is a process, entity, or data store. that has no outputs, only inputs.

Question 25

What are semantics errors in a data flow diagram?

Answer 25

Semantics errors in a data flow diagram are any misunderstandings by the analyst in collecting, analyzing, and reporting information about the system. Basically, something that is misrepresented.