Classical Software Engineering

Computing

Quiz 12 :

Classical Analysis

Quiz 12 :

Classical Analysis

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Use a Petri net to specify the circulation of a single book through the library of Problem 8.7. Include operations H, C, and R in your specification.
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Petri net technique is used in performance evaluation, operating system and software engineering. It helps in specifying concurrent interrelated activities. This technique can be used for system which have potential timing problem such as synchronization problem, race condition, deadlock. A petri net consists of four parts
• A set of places P (p 1 , p 2 … p n )
• A set of transition T (t 1 , t 2 … t n )
• An Input function I (I: T, mapping from transition to Places)
• An output function O (O: T, mapping from transition to Places)
Petri net technique specifying the circulation of single book through the library is as follows:
• A product is to be installed to issue a book to a borrower.
• A book is represented by a token
• A token in
img denotes that the book is issued to the borrower.
• Book should not be on hold if it is to be issued to the borrower. These illuminate when borrower query for book it causes the book checking to be done. The illumination is cancelled when the book is not on hold and can be issued or when the book is on hold and cannot be issued to the borrower.
• A token in
img denotes that the Book is in the collection.
img • When borrower asks for a book is illuminated, transition "Book Check C" is enabled and then fired.
• If the book is not on hold, the token in
img is removed and a new token appears in
img . Book will be marked as hold and token form
img will appear in
img • This brings the book from check state to book issue state.
• If the book is on hold but returned by the borrower, the token from
img is removed and a new token appears in
img and then in
img . Book will be marked as hold and token form
img will appear in
img

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A fixed-point binary number consists of an optional sign followed by one or more bits, followed by a binary point, followed by one or more bits. Examples of fixed-point binary numbers include 11010.1010, -0.000001, and +1101101.0 More formally, this can be expressed as img (The notation [... ] denotes an optional item, and a | b denotes a or b.) Specify a finite state machine that will take as input a string of characters and determine whether or not that string constitutes a valid fixed-point binary number.
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Finite State Machine (FSM):
• FSM has a set of states and transition condition that are used to design a logical circuit as well as software programs.
• At any given time the machine can be in only one state called the current state. The FSM can change its current state to other state on triggering a condition.
• In general, a FSM has 5 tuple (J, K, T, S, F) where,
o J - set of non empty states
o K- set of inputs
o T- transition function
o S- initial state
o F- set of final states
FSM to determine the input is valid fixed point binary number:
The FSM to accept the valid fixed point binary numbers consists of 5 tuples (J, K, T, S, F).
Where,
• "J" is the set of states consists of {Enter, Sign, Bit String, Binary Point, Accept Number, and Reject Number}.
• "K" is the set of inputs consists of {+, -, 0, 1,. }.
• "T" indicates the transition function is given as,
img • "S" indicates the initial state "enter".
• "F" indicates the final state is {Accept Number, Reject Number}.
The state diagram to accept the valid fixed point binary numbers is as given below:
img Explanation:
• The initial state is "Enter".
• On giving the input either "+" or "-" to the Enter state, the machine goes into "Sign" state.
• If the input to the "Enter" state is either "0" or "1", the machine goes to "Bit String" state.
• Any other input to the "Enter" state leads to rejection of the binary number.
• If the input to the "Sign" state is either 0" or "1", the machine goes to "Bit String".
• Any other input to the "Sign" state leads to rejection of the binary number.
• If the input to the "Bit String" state is either 0" or "1", the machine stays in 'Bit String" state itself.
• If the input to the "Bit String" is ".", the machine goes to "Binary Point".
• Any other input to the "Bit String" state leads to rejection of the binary number.
• If the input to the "Binary Point" state is either "0" or "1", the machine goes into "Accept Number" state.
o Any other input to the "Binary Point" state leads to rejection of the binary number.

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Complete the specification document for the library circulation system of Problem 8.7 using Gane and Sarsen's technique. Where data have not been specified (for example, the total number of books checked in and out each day), make your own assumptions, but make sure that they are indicated clearly.
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Gane and Sarsen is a popular technique to specify software using graphics. It is a structured system analysis which goes through nine steps to analyse the need of the client. Specification of library circulation system using Gane and Sarsen technique is as follows:
Step1- Draw the DFD:
Data flow diagram is a pictorial representation of logical data flow of the requirements. Stepwise refinement can also be done in the DFD. Data flow analysis is shown below:
img Step2- Decide what section to computerize and how:
All the flow of data shown in the DFD needs to be computerized. What to computerize will depend upon the client budget for which cost benefit analysis can be done.
Step3-Determine the details of the data flow:
It determines what data items must go into the various data flows.
-Book: Book_number/Id, Author, Title, Subject, Hold details
-Borrower: borrower id, books hold
-Catalogue: Book_number/id, author, title, subject
-Hold book: borrower number
Step4-Define the logic of the processes:
It determines what each process does.
Add book
-adds book details to book collection/storage
Remove book
-scans the book number and deletes book details from book collection
Book checking
-scan book id and borrower id
-check if book is not hold
-update book collection/storage with book hold by borrower id
Book hold
-scan book id and borrower id
-check if book is not hold
-if not update book collection/storage with book hold by borrower id
Catalogue data
-accepts query
-search data
-give result of query
Step5- Define data storage:
It determines the storage required for each content.
Book collection (512 bytes-assumed)
-Book number, Author, Title, subject, book hold, borrower number
Step6- Define the physical resources:
It determines file type, size etc. for each content.
-index sequential file for book collection
-Primary index file for book id and borrower id
-secondary index for author, title and subject
Step7-Determine input/output specification:
It determines the screens for the various modules.
Input screen for- add book, remove book, search book from catalogue.
Output screen for- catalogue information
Reply screen for- add book, remove book, search book, return book, remove book
Step8- Perform sizing:
It is assumed that there are 200,000 books in the library collection which will require 150 MB for catalogue information, 15 MB will be required for index and 2 MB will be required for the software installation.
Step9- Determine hardware required:
-CPU with 2 GB hard disk
-A backup system
-Four terminals for borrowers
-Four terminals for librarian

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Why is it so important that the specification document should have no omissions, contradictions, or ambiguities?
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What are the weaknesses of informal specifications?
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What are the strengths of informal specifications?
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(Term Project) Using the technique specified by your instructor, draw up a specification document for the Chocoholics Anonymous product described in Appendix A.
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Correct the specification paragraph of Section 12.2 to reflect the client's wishes more accurately.
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Why should the following constraints not appear in a specification document? (i) The product must significantly reduce transportation expenses that arise from distributing our beer in central Queensland. (ii) The credit card database must be set up at a reasonable cost.
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Draw a data flow diagram for the specification you drew up for Problem 12.8. Ensure that your DFD simply reflects the flow of data and that no assumptions regarding computerization have been made.
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Why are many software organizations reluctant to use formal specifications?
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A floating-point binary number consists of an optional sign followed by one or more bits, followed by the letter E, followed by another optional sign, followed by one or more bits. Examples of floating-point binary numbers include 11010E-1010, -100101E11101, and +1E0. More formally, this can be expressed as img (The notation [...] denotes an optional item, and a | b denotes a or b.) Specify a finite state machine that will take as input a string of characters and determine whether that string constitutes a valid floating-point binary number.
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You are a software engineer working for a large company that specializes in computerizing library systems. Your manager asks you to specify the complete library circulation system of Problem 8.7 using Z. What is your reaction?
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Use the finite state machine approach to specify the library circulation system of Problem 8.7.
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Use mathematical formulas to represent the specification paragraph of Section 12.2. Compare your answer with your answer to Problem 12.4.
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Write a precise English specification for the product to determine whether a bank statement is correct (Problem 8.8).
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Consider the automated library circulation system of Problem 8.7. Write down precise specifications for the library circulation system.
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Draw a data flow diagram showing the operation of the library circulation system of Problem 8.7.
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Consider the following recipe for grilled pockwester. Ingredients: img The night before, take one lemon, squeeze it, strain the juice, and freeze it. Take one large onion and three shallots, dice them, and grill them in a skillet. When clouds of black smoke start to come off, add 2 cups of fresh orange juice. Stir vigorously. Slice the lemon into paper-thin slices and add to the mixture. In the meantime, coat the mushrooms in flour, dip them in milk, and then shake them in a paper bag with the bread crumbs. In a saucepan, heat 1/2 cup of Pouilly Fuisse. When it reaches 170°, add the sugar and continue to heat. When the sugar has caramelized, add the mushrooms. Blend the mixture for 10 minutes or until all lumps have been removed. Add the eggs. Now take the pockwester, and kill it by sprinkling it with frobs. Skin the pockwester, break it into bite-sized chunks, and add it to the mixture. Bring to a boil and simmer, uncovered. The eggs previously should have been vigorously stirred with a wire whisk for 5 minutes. When the pockwester is soft to the touch, place it on a serving platter, sprinkle with Parmesan cheese, and broil for not more than 4 minutes. Determine the ambiguities, omissions, and contradictions in the preceding specification. (For the record, a pockwester is an imaginary sort of fish and frobs is slang for generic hors d'oeuvres.)
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Show how your solution to Problem 12.15 can be used to design and implement a menu-driven product for the library circulation system (Problem 8.7).
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