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Introduction to Database File Formats • Comma delimited file – – – – "s1","peter",3 "s2","paul",2.5 "s3","mary",3.5 Demo: Excel – Data/Import • Extended Markup Language (XML) document • Spreadsheet list • Database table XML <?xml version="1.0" ?> <Books> <Book> <ISBN>1-34567-04-01</ISBN> <Authors> <AuthorName>John Smith</AuthorName> <AuthorName>Peter Chen</AuthorName> <AuthorName>David Chao</AuthorName> </Authors> <Price> $45.00</Price> <Description>This is a grerat book</Description> </Book> <Book> <ISBN>1-34567-04-02</ISBN> <Authors>Adam Smith</Authors> <Price> $25.00</Price> <Description>This is a second great book</Description> </Book> </Books> File Concepts • File consists of a group of records. Each record contains a group of fields. • Example: Student file – – – – SID S1 S3 S5 Sname Peter Paul Mary Major CIS ACCT CIS Sex M M F GPA 3.0 2.7 3.2 File Concepts • Each file must have one key field. Key field uniquely determines a record in a file. – Simple key, composite key • Grouping field: A filed that can be used to group records, for example, Major in the Student file. • Calculated filed: A field whose value is derived from existing fields, for example, Age can be calculated from DateOfBirth. • Each field can hold only one value. Calculated Field Example (1) • DateOfBirth -> Age • Date functions: – – – – Now Today Year Etc. • Age = Calculated Field Example (2) • Salary field -> IncomeGroup – Salary<=40000, -> Low – 40000 <Salary <=70000, -> Median – Salary > 70000, -> High Which field is the key field? File Organization and Access • Sequential file (heap file): Records are organized in sequence in the order in which they are entered. • File access: – Sequential access – Direct access • Index file: Key + record’s location (address) Direct access time • 1. Seek time: This is the time needed to mechanically position the read/write head on the correct track. • 2. Rotational delay: This is the time needed to wait for the beginning of the required block to rotate into position under the read/write head • 3. Data transfer time: Time needed to transfer the data. Database Concepts • A database is a collection of related files. – Support business operations – Provide information Database Management System • A database management system (DBMS) is a software that enables users to create and maintain a database. Major Functions of Database Management • Creating a database – Analysis: Entity-Relationship Diagram – Design: Design file structure – Implementation • Accessing a database • Updating a database Database design objectives • Eliminate data duplication. Example: – Student file: SID, SNAME, ADDR, MAJOR, GPA – Student Account File: SID, SNAME, ADDR, BALANCE • Link related records in the related tables. An Example of Database • Department, Employee: – Each department has many employee, and each employee works for one department. • Design a database so that we can: – Find which department David Chao works for. – Find all the employees that work for the Personnel department. Entity-Relationship Diagram • Entity (Entity set): a set of similar objects. • A business environment may involve many entities. – University: Faculty, Student, Course – Customer, Employee, Order • A business operation may involve more than one entities. – Faculty teach Course, Faculty advise Student – Customer open Account, Customer purchase Product. Relationship • Relationship: Interaction between entity types. – Faculty teach Course, Faculty advise Student – Customer open Account, Customer purchase Product. • Binary relationship: A relationship involves two entity types. Three kinds of Binary Relationship • 1:1 – Each student has one account – Each account belongs to one student • 1:M – Each college has many departments – Each department belongs to one college • M:M – Each student can take many courses – Each course can be taken by may students Student 1 Has 1 Account M Enroll M Course Faculty Department Attributes • Properties of an entity or a relationship. – Student: SID, Sname, DateOfBirth • Primary key • Derived attributes: – Age SID Sname Phone DateOfBirth Age Student Database Design Demo • Each entity translates to a table. • Relationships are implemented by foreign key or relationship table. • Example 1: University database • Example 2: Customer/Orders Implementation with Access • Access objects: – Tables • • • • – – – – Open Design New Wizard Queries Forms Reports Pages Creating a Table • Create table in design view – Field name – Field data type • Create table by using wizard • Create a primary key • Enter data Querying Database