Library Management System-Software Engineering-Lecture 17 Slides-Computer Science, Slides of Software Engineering

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LECTURE 17: LIBRARY CASE STUDY

Software Engineering

1 A Library Management System

• In this lecture, we specify a simple library system.
• Operations: - check out a book; - return a book; - add a book to library; - remove book from library; - get list of books by author or subject area; - get list of books checked out by particular borrower;

1.1 Types

• We need sets for: - all possible books; - all possible copies of books; - all possible people; - all possible authors; - all possible subjects; - the various reports that may be produced.
• So parachute in:

[BOOK, COPY, PERSON, AUTHOR, SUBJECT, REPORT]

1.2 State Space

• The state space is describes in several steps. First, a schema containing information relating to books in the library.

ParaLibrary instance of : COPY → 7 BOOK written by : BOOK → 7 IP AUTHOR about : BOOK → 7 IP SUBJECT dom written by ⊆ ran instance of dom about ⊆ ran instance of

• The database part of the schema is as follows:

LibraryDB borrower, staff : IP PERSON available, out : IP COPY borrowed by : COPY → 7 PERSON borrower ∩ staff = ∅ available ∩ out = ∅ dom borrowed by = out ran borrowed by ⊆ borrower ∀p : borrower • #borrowed by∼(|{p}|) ≤ MaxCopies

• borrower is the set of all borrowers known to the system;
• staff is the set of all staff known to the system;
• available is the set of all available books;
• out is the set of borrowed books (i.e., ones that have been checked out);
• borrowed by tells us who borrowed the books out on loan.

• The library state space is then as follows:

Library ParaLibrary LibraryDB dom instance of = available ∪ out

• the only invariant in this schema tells us that the library does not know anything about books which are not in stock.

1.3 The Operations

• We assume initialisation operations; these are trivial.
• First we look at checking out books...
• Inputs: person name (n?) and copy (c?).

CheckOut ∆Library n? : PERSON c? : COPY n? ∈ borrower c? ∈ available #borrowed by∼(|{n?}|) < MaxCopies available′^ = available \ {c?} out′^ = out ∪ {c?} borrowed by′^ = borrowed by∪ {c? 7 → n?}

1.4 Returning a Book

• One input: the copy to be returned.

Return ∆Library c? : COPY c? ∈ out available′^ = available ∪ {c?} out′^ = out \ {c?} borrowed by = {c?} −
borrowed by

• precondition states that the book can only be returned if it is out;
• 1st post-condition says that the book is available after the operation;
• 2nd post-condition says that the book is no longer out;
• 3rd post-condition uses domain subtraction to remove the correct record from the borrowed by function.
• For example,

borrowed by = {b 01 7 → mjw, b 02 7 → en, b 03 7 → mjw} {b 01 } −
borrowed by = {b 02 7 → en, b 03 7 → mjw}

AddNewBook ∆Library c? : COPY b? : BOOK a? : IP AUTHOR s? : IP SUBJECT

b? 6 ∈ ran instance of c? 6 ∈ available ∪ out

available′^ = available ∪ {c?} instance of ′^ = instance of ∪ {c? 7 → b?} written by′^ = written by ∪ {b? 7 → a?} about′^ = about ∪ {b? 7 → s?}

AddAnotherCopy ∆Library c? : COPY b? : BOOK

c? 6 ∈ available ∪ out b? ∈ ran instance of

available′^ = available ∪ {c?} instance of ′^ = instance of ∪ {c? 7 → b?}

RemoveOther ∆Library c? : COPY c? ∈ available #(instance of ∼(|{instance of (c?)}|)) > 1 available′^ = available \ {c?}

• Note that there is no need to alter any variables in ParaLibrary; we only change available, to indicate that the book is no longer available.

RemoveLast ∆Library c? : COPY

c? ∈ available #(instance of ∼(|{instance of (c?)}|)) = 1

available′^ = available \ {c?} instance of ′^ = {c?} −
instance of written by′^ = {instance of (c?)}−
instance of about′^ = {instance of (c?)} −
about