What is meant by Statistical Usage Testing?

Statistical usage testing is the testing process that is aimed at the fitness of the software system or application.

The test cases chosen for carrying out statistical usage testing mostly consist of the usage scenarios and so the testing has been named as statistical usage testing. Software quality is ensured by the extensive testing but that has to be quite efficient. Testing expenditures covers about 20 – 25 percent of the overall cost of the software project. In order to reduce the testing efforts, deploy the available testing tools since they can create automated tests. But usually what happens is that the important tests require manual intervention with the tester requiring thinking about the usage as well behavior of the software. This is just the repetition of the tasks that were done during the requirements analysis phase.

About Statistical Usage Testing

- A usage model forms the basis for the creation of tests in statistical usage testing.

- Usage model is actually a directed usage graph more like a state machine and it consists of various states and transitions. 

- Every transition state has a probability associated with it regarding the traversal of the transition when the system would be in a state that marks the beginning of the transition arc. 

- Therefore, the sum of the probabilities of outgoing transitions sum up to unity for every state.

- Every transition can be associated with an event and more with parameters that are known to trigger the particular transition. 

- Such event associated transitions can be further related to certain conditions called the guard conditions. 

- These conditions imply that the transition occurs only if the value of the event parameter satisfies the condition.

- For assigning probabilities to the transitions, 3 approaches have been defined as follows:

1. Uninformed approach: In this approach, same probability is assigned to the exit arcs of a state.
2. Informed approach: In this approach, a sample of user event sequences for calculating suitable properties. The sample is captured from either an earlier version of the software or its prototype.
3. Intended approach: This approach is used for shifting the focus of the test to certain state transitions and for modeling the hypothetical users.

- According to a property termed as the marcov property, the actual state is what on which the transition probabilities are dependent. 

- However, they are independent of the history again by the property. 

- This implies that the probabilities must be fixed numbers. 

- A system based up on this property is termed as a marcov chain and it requires conclusion of some analytical descriptions. 

- Usage distribution is one among such descriptions. 

- It gives for every state its steady–state probability i.e., appearance rate that is expected.

- All the states are associated to one or the other part of the software system or application and the part of the software that attracts more attention from the tests is shown by the usage distribution. 

- Some other important descriptions are:

1. Expected test case length
2. Number of test cases required for the verification of the desired reliability of the software system or application.

- The idea of the usage model generation can be extended by handling guard conditions and enabling the non–deterministic behavior of the system depending on the state of the system’s data. 

- All this helps towards the application of the statistical usage testing to systems over a wide range. 

- The use cases are defined by the top–level structure of the unified modeling language (UML). 

How is data understood through reverse engineering?

Reverse engineering forms an internal part of the whole software re- engineering process. To implement the reverse engineering properly in the re- engineering process one needs to understand the data through the reverse engineering.

In this article we have taken up the same topic i.e., “how is data understood through reverse engineering?” 

- When the reverse engineering is carried out, the main objective is always to recover the designs and specifications of the software system or application.

- With reverse engineering, the development is only understood and no changes are made to the software system or application. 

- For the reverse engineering process, the source of the software system or application is fed as the input. 

- If you go through the history of the reverse engineering, you will find some cases where the executable code is given as input for the reverse engineering process. 

- The reverse engineering though being in a great contrast with the re- engineering forms an internal part of it. 

- Reverse engineering serves the purpose of recovering system design and specifications in the software re- engineering process model. 

- These recovered designs and specifications are used by the engineers to understand the software system or application before they start re- organizing the whole structure.

- However, there have been cases in which the reverse engineering is not always followed by the re- engineering process. 

- There are three stages in reverse engineering process.

 1. System to be re- engineered is subjected to automated analysis.

 2. Then it is manually annotated.

 3. With the system information obtained, a whole set of new documentation is generated containing:

(a)  Program structure diagrams

(b)  Data structure diagrams and

(c)   Traceability matrices.

Activities in Reverse engineering

In reverse engineering the data is understood by the 3 basic activities that involved intense understanding efforts:

1. Understanding process: In order to understand the procedural abstractions as well as functionality analyze the source code on the level:

(a)  System

(b)  Program

(c)   Component

(d)  Statement and

(e)  Pattern

2. Understanding data: It analyzes the internal data structures and data base structure.

3. User interfaces: It analyzes the basic actions processed by the interface, system’s behavioral response to those actions and equivalency of the interfaces.

More about reverse engineering....

- The beginning of the reverse engineering process is marked with an analysis phase in which the analyzation is carried out with the help of automated tools in order to discover the structure of the software system or application. 

- But this stage itself does not suffice the purpose of recovering the whole structure. 

- Engineers then have to work on the program code and model and add the recovered information to this.

- The recovered information is maintained in form of a directed graph. 

- The engineers always make it a point to link the directed graph to the source code. 

- The directed graphs are compared with the code with the help of the information browser stores. 

- This graph helps in generating trace ability matrices and the data structures. 

- Tools that are used make it easy to navigate through the code. 

- After the complete generation of the design documentation, the information store is supplied with the additional information as a measure to re create the specifications systems. 

What is meant by Software Reengineering Process Model?

Software re- engineering process model is based up on the principles of the software re- engineering that was proposed by Chifosky in the year of 1990.  Before we discuss about the software re- engineering process model let us see what software re- engineering is.

What is Software Re-engineering?

- The software re- engineering is considered to be a process that alters a software system and thus reconstituting it in to a new form that is better than its previous form.

- The process of the re- engineering usually occurs after the software system or application has been reverse engineered. 

- The re- engineering is also carried out for the addition of the new functionalities or to correct the discovered faults and errors. 

- Sometimes this whole process is often collectively called as reverse engineering. 

But there is a subtle difference between the two! 

- The former process i.e., the reverse engineering is like an initial examination of the software system and the latter is like the subsequent modification. 

- Re- engineering of the software systems often comes in to play where there is an involvement of a legacy system. 

- In such cases the re- engineering can be considered to be a process that re- structures a legacy system in to a new system that is constituted of much better features and functionality and maintain the quality constraint.

Re- engineering is not a thing that can be achieved in an instant rather it takes a lot of time since there is a utilization of many information technological resources over the years. Therefore every organization requires a well defined strategy for carrying out the software re-engineering. 

Steps in Software re-engineering process model

The software engineering process model consists of the following steps:

1.Inventory analysis: Analysis of all the active applications listed in the inventory of an organization.

2.Document reconstruction: The software systems that are business critical are re- documented.

3. Reverse engineering

4. Code restructuring: It involves the analyzation of the source code and reviewed again.

5. Data restructuring: It begins with reverse engineering and ends with the review of all the data structures.

Scenario behind software re-engineering process

- Software re- engineering process serves the purpose of bringing up the poorly documented and poorly structured code to a standard that is maintainable and acceptable. 

- Let us see the scenario behind the need of re- engineering. 

- In a code that is poorly controlled and maintained, lies either a large number of files spread over a number of locations or consists of only a single file consisting of a very lengthy code.

- Observing these files, one could notice that the comments do not appear to have any relationship with the code itself and the associated documentation has become outdated or refers to the previous versions of that software system or application that has underwent many modifications since then which were left undocumented. 

- To say, an executable file does exists but many decisions have to be taken to run it. 

- At this point the identification of the actual objectives of the software re- engineering process becomes important. 

- There might be so many problems underlying those decisions that now can be easily addressed. 

- It is very important that before beginning with the re- engineering of the whole code that you check its correctness otherwise you will suffer a major set back if you would have been re- engineering the wrong code all the time. 

- At the end of the process the final code needs to be base-lined with the associated project log and the documentation.

- The re- engineered software system or application is brought to a well defined stage at which it can be considered to be ready for the release and also its future maintenance will be less arduous.