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Summary (continued) Structure charts may be based on three-layer architecture Modules will be clearly identified by layer Structure chart may be decomposed if layers execute on multiple systems Structured design may also include: System flowcharts to show data movement Module pseudocode to describe internal logic of structure ch...
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Summary (continued) Determine what alternatives are possible for developing solution Implementation alternatives include: Building system in-house Buying packaged or turnkey solution Contracting with developer to build it (outsource) Develop recommendations and present to management to make funding decisions
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Summary (continued) Models from IE may supplement DFDs Process decomposition diagram (how processes on multiple DFD levels are related) Process dependency diagram (emphasizes interaction with stored entities) Location diagram (geographic where system used) Activity-location matrix (which processes are implemented at which location...
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Summary (continued) Things are what user deals with and system remembers, such as customer placing an order Traditional approach uses entity-relationship diagrams (ERD) for data entities, attributes of data entities, and relationships between entities Things are shown as data entities Object-oriented approach uses class diagrams for...
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Control structure Example: SELECT ProductID, Quantity, UnitPrice, [discount%]= CASE WHEN Quantity <=5 THEN 0.05 WHEN Quantity BETWEEN 6 and 10 THEN 0.07 WHEN Quantity BETWEEN 11 and 20 THEN 0.09 ELSE 0.1 END FROM [Order Details] ORDER BY Quantity, ProductId
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Insert, delete, and update The UPDATE Command: to modify attribute values of one or more selected tuples. a WHERE clause in the UPDATE command selects the tuples to be modified from a single relation. However, updating a primary key value may propagate to the foreign key values of tuples in other relations if such a referential triggere...
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Mapping EER Model Constructs to Relations Step 9: Mapping of Union Types (Categories). For mapping a category whose defining superclass have different keys, it is customary to specify a new key attribute, called a surrogate key, when creating a relation to correspond to the category. In the example below we can create a relation OWNER t...
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Tuple Relational Calculus The tuple relational calculus is based on specifying a number of tuple variables. Each tuple variable usually ranges over a particular database relation, meaning that the variable may take as its value any individual tuple from that relation. A simple tuple relational calculus query is of the form {t | COND(t)} w...
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In-Class Exercise Consider the following relations for a database that keeps track of student enrollment in courses and the books adopted for each course: STUDENT(SSN, Name, Major, Bdate) COURSE(Course#, Cname, Dept) ENROLL(SSN, Course#, Quarter, Grade) BOOK_ADOPTION(Course#, Quarter, Book_ISBN) TEXT(Book_ISBN, Book_Title, Publisher, ...
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Cardinality Constraints Cardinality Constraint: Quantification of the relationship between two concepts or classes (a constraint on aggregation) MINIMUM (A,B) = n: At a minimum, one instance of A is related to at least n instances of B. n = 0 MIN(A,B) = 0 MIN(Person, Car) = 0 n = 1 MIN(A,B) = 1 MIN(Cust, Ship-address) = 1 n = inf. MIN(A,B...
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