Introduction to Database ISYS 363

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

Examples Database file –Created and managed by a DBMS Spreadsheet file –Created and managed by a spreadsheet software XML file Comma-Delimited file – A text file that can be processed by any programming languages, DBMS and spreadsheet. –"s5","peter",3.5 –"s1","paul",3 –"s7","mary",2 Comma-Delimited file demo: stdata.txt –Access – File/Get External Data/Import –Excel – Data/Import External Data/Import Data

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

Relational Database Data is logically structured within relations. Each relation is a table (file) with named columns (attributes, fields) and rows (records).

File Concepts Each file must have one key field. Key field uniquely determines a record in a file. 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.

Basic File Processing Excel Demo Sorting/Grouping Compute subtotals –Chart using subtotals Selecting records meeting criteria –Filter –Custom filter

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.

Other file organization Hash file (direct file) –Hashing function, H –Record location = H(key) –Search a record with key K1: Location of record with key K1 = H(K1)

Database Concepts A database is a collection of related files. –Support business operations –Provide information A database management system 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. –Inconsistent data, double entry, waste space Link related records in related tables. Example: –StudentTable: SID, Sname, Address, Major, –StudentAccountTable: SID, Sname, Address, Balance Example: –Company Database Department table: DID, Dname, DepOffice, DepPhone Employee table: EID, Ename, Address, , Salary Note: A table’s key field plays an important role in linking related records.

Design a database for a company to keep track of employees, departments and projects. The company is organized into departments. Each department has a unique number, name. Each department controls a number of projects, each of which has a unique number, and name. Several employees may work on the same project. We store each employee's SSN, name, address, salary, and birthday. An employee is assigned to one department but may work on several projects. An example of database design problem

Entity-Relationship Diagram An entity is a “thing” in the real world, such as a person, place, event for which we intend to collect data. An entity has certain characteristics (properties) known as attributes (fields). Entity type(Entity set): a set of similar entities. A business environment may involve many entity types. –University: Faculty, Student, Course –Department, Employee, Dependent –Sales person, Customer, Order

Entity-Relationship Diagram 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 types of binary relationship: –1:1, 1:M, M:M