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 John Smith Peter Chen David Chao $45.00 This is a grerat book Adam Smith $25.00 This is a second great book

File Concepts File consists of a group of records. Each record contains a group of fields. Example: Student file –SIDSnameMajorSexGPA –S1PeterCISM3.0 –S3PaulACCTM2.7 –S5MaryCISF3.2

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 Low –40000 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 Account Has 11 Course Enroll M M Faculty Department

Attributes Properties of an entity or a relationship. –Student: SID, Sname, DateOfBirth Primary key Derived attributes: –Age

Student SID Sname Phone DateOfBirth Age

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