Q1 - What is a primary Actor in a Use-Case? How is it drawn in the diagram? How
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Question
Q1 - What is a primary Actor in a Use-Case? How is it drawn in the diagram? How is that same actor represented in the DFD diagram?
Q2- What is the relationship between level 0 and level 1 DFD diagrams? Cite steps in Building DFDs hierarchy
Q3- Suppose you are in the process of drawing the DFDs, and you have found that one of your Level 1 DFD describing a process in level 0, has more than 8 sub-processes. What does that indicate? And How do you fix it?
Q4- Read the following case study description and answer the questions given below. Consider a system for buying a new car. The customer should inspect the vehicle and chose the type, the color and the desired characteristic. If the customer finds his suitable vehicle, he gives his personal information to the vendor, then signs a sales contract. Before the final sale contract is delivered to the customer, the payment must be collected. At the end the transaction details must be recorded by the vendor.
a) Write a Use Case “Buy a new Car” by filling in the specific template. [8 points]
b) Draw a use case diagram for describing the functional requirements of the above system.
Q5- Perfect Pizza wants to install a system to record orders for pizza and chicken wings. When regular customers call Perfect Pizza on the phone, their phone number goes automatically into the Pizza system. Also the name, address, and other customer information come automatically up on the screen. Once the order is taken, it is given to the cook. A receipt is printed. Weekly totals and statistics are kept for comparison with the management department. Question: Draw a context level diagram for PERFECT PIZZA
Explanation / Answer
Q 1.
Use cases: A use case describes a sequence of actions that provide something of measurable value to an actor and is drawn as a horizontal ellipse.
Actors: An actor is a person, organisation or external system that plays a role in one or more interactions with your system. actors are drawn as stick figures.
Primary Actor: The primary actor of a use case is the stake holder that calls on the system to deliver one of its services. It has a goal with respect to the system - one that can be specified by its operation. The primary actor is often, but not always, the actor who triggers the use case.
Actor(DFD)
An actor produces and consumes data, driving the DFD.Actors lie on the boundary of the diagram; they terminate the flow of data as sources and sinks of data. They are also known as terminators. Data flows between an actor and a diagram are inputs to and output s of the diagram. The system interacts with people through the actor. They are also known as terminators.
Q 2.
Level 0 DFD(Context Level DFD):
A context level DFD is the most basic form of DFD. It aims to show how the entire system works at a glance. There is only one process in the system and all the data flows either into or out of this process. Level 0 DFD’s demonstrates the interactions between the process and external entities. The do not contain data stores.
When drawing Context level DFD’s , you must identify the process, all the external entities and all the data flows. You must also state any assumptions you make about the system. You then draw your external entities in the corners and finally connect your entities to your process with the data flows.
Level 1 DFD:
Level i DFD aim to give an overview of the full system. They look at the system in more detail. Major processes are broken down into sub-processes. Level 1 DFD also identifies data stores that are used by the major processes.
When constructing a Level 1 DFD, you must start by examining the Context Level DFD. You must break up the single process into its sub-processes. You must then pick up the data store. Like the Context Level DFD, all entities, data stores and processes must be labelled.
Q 3.
Each process in Level 0 may in turn be exploded to create more detailed child diagram. The primary rule for creating child diagrams, vertical balancing dictates that a child diagram cannot produce output or receive input that the parent processes does not also produce or receive. All data flow not or out of the parent processes must be shown flowing into or out of the child diagram.
Processes may or may not be exploded , depending on their level of complexity. When a process is not exploded, it is said to be functionally primitive and is called a primitive process. Logic is written to describe these processes.
Thus as per in per question Level 1 DFD describing a process in level 0, has more than 8 sub-processes will be complex and will not be exploded rather logic has to be written to describe this process.
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