Figure 6.5 A simple nite state machine. in Visual Studio .NET

Generate QR Code 2d barcode in Visual Studio .NET Figure 6.5 A simple nite state machine.
Figure 6.5 A simple nite state machine.
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Figure 6.6 A simple state machine of a log-in process.
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This is quite a descriptive diagram as it shows the sequences of possible actions that the system undergoes initially the user starts at the Start state and logs in. This takes them to the Check name state, and if the username is not recognized, the system returns through the fail transition to the Start state. If the name is registered, the user is then prompted for a password, which is then checked. Again the log-in will fail if this is not correct. Otherwise the user is into the main part of the system. The problem is that it is not a proper nite state machine for a number of reasons: 1 The user inputs are sequences of symbols rather than a single symbol. 2 The output is not speci ed in the diagram. 3 The Check name and Check password states hide a lot of invisible behavior; in particular, the machine needs to look up information in some database or similar memory component. Thus nite state machines are not powerful enough for our purposes. There are other, more powerful machines that can be used, for example, pushdown machines are popular in theoretical computer science courses. They contain a simple stack like memory that can be used to do more sophisticated things such as to recognize certain types of formal languages (context-free languages). Furthermore, nite state machines tend to be too low level for practical use, but a generalization of these has been developed based on ideas of a famous mathematician of the 1970s (Samuel Eilenberg). This will be discussed in the next section. Our approach is to apply this extremely powerful modeling paradigm that seems to be fairly easy to use and has proven excellence in the construction of functional test sets.
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6.5 Extreme Modeling (XM)
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EXTREME MODELING (XM)
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It makes a lot of sense to have a simple and lightweight method of describing the system or parts of a system in terms of what it does and the order in which it does it. If we have such a picture, we will be able to use it to de ne test sets that do more than just test one simple function. The extreme X-machine (XXM) is a suitable candidate. These were introduced by Thomson (2003, 2005), and we have been using these for a number of years with great success. They are popular with programmers, and customers can also make sense of them. The simple machine of the type in Fig. 6.6 is called an X-machine by Eilenberg (1974) and is discussed at length in Holcombe (1998). It can be used to describe many things, but it is not always convenient. One problem is that each state transition (indicated by an arrow) needs to be triggered by an external input or event. Sometimes, especially in object-oriented programs, we would like to allow the system to call some other function or method without an explicit external input. Thus we might have the diagram shown in Fig. 6.7. Here the input from a potential user is supplied in one go, by completing a simple form, and the Validate user state then generates a result that triggers one of the three transitions Fail, User access, or Admin access internally. The operations that are labeling the transitions (arrows) represent functions of various levels of complexity. The real power of these machine diagrams is that they can be hierarchical. In other words, the functions labeling the transitions can themselves be broken down into a series of operations at a lower level described by a subsidiary machine.
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Figure 6.7 A simple XXM.
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Figure 6.8 A detailed XXM model of the transition Username & password in Fig. 6.7.
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Thus the Username & password function could be de ned in another diagram (Fig. 6.8). In this system, consider what happens in the Check password state. There are three possible transitions from this state: The password is okay and the user has Admin privileges. The password is okay and the user has User privileges. The password fails, and if this happens three times, the error state is reached, and a message is displayed on the screen stating this. There are no other possibilities and so the system will be fully de ned at this point. In some cases, you may nd a state where there could be cases that have not been speci ed in these cases it is important to decide what the system should do it might ignore an input and remain in the same state, for example, or raise an error and transfer to an error state from which some suitable recovery is de ned. Now consider the bene ts for testing. As soon as you have de ned an XXM, it is possible to de ne some testing sequences. An obvious strategy is to design test sets that will trigger each transition either singly or in sequences derived from the diagram. For Fig. 6.8, the following operational sequences can be de ned, immediately. 1 Display Login (essentially running the program from the beginning) 2 Username & password 3 Admin access 4 User access We are using the labels of the transitions to denote these sequences. We need to consider the Fail transitions, also. Thus a set of test sets can be constructed to do this.
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6.5 Extreme Modeling (XM) Table 6.1 Basic Data for Some Tests Name User1 User2 User3 User4 Password Pass1 Pass2 Pass3 Pass4 Administration rights Admin Admin no no
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Suppose we de ne a set of users with passwords some with admin access (Table 6.1). We need also to de ne some other strings to represent invalid users to the system. Now we can set up a simple set of tests to see whether the entire machine is implemented correctly in the implementation of the story. Thus a test such as ,User1. ; ,Pass1. should result in getting to the Admin section initial screen. However ,User1. ; ,Pass2. should produce a failure, which returns the system to the Start screen. Thus the strategy is to make sure that every path through the machine (a path is a sequence of transitions taken one after the other) is explored and tested. The model thus far discussed puts the main focus on the control of the software what can be done and when. Software, however, consists of two principle elements: control and data. They are intimately linked together one without the other tends to provide an incomplete view of things. In languages such as UML, there are diagrams and notations that can describe the control (e.g., statecharts), and there are diagrams that describe data (often from an implementation point of view such as class diagrams together with local methods). In the approach taken here, we have a tighter link between the two aspects. The XXM diagrams show the ow of control in the system; the states divide up the system in such a way that the operations are managed in a suitable way. But what do these operations do They process data, and it is here that we can introduce the type of data that is important to the application. The example discussed above involves data in some kind of database. Thus the operations in the system manipulate this database uploading information, querying information, and deleting information. Each of the operations can be de ned in terms of what it does to the database state. In another example, consider a word processor. Here the operations will manipulate text, inserting sections of text into an existing document, formatting parts of the document, saving and opening text les, and so on. The data can be described in very general terms as a set of sequences of characters or symbols, including spaces. In a rather simplistic way, we could describe the state of a document as consisting of three sequences: ,sequence1. , ,sequence2 . , ,sequence3.
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