Transcript database
EAK 362/2 MIS LECTURE 4 PART 1 DataBase Management Systems Introduction to Database Technology Database An organized collection of logically related data. •Usually owned by a single enterprise or organization •Contain facts the enterprise or organization cares about The data items can be text, numbers, dates, sound file, music, v among others. Database System A database system is essentially nothing more than a computerized record-keeping system. Many of the data files traditionally kept on paper or in flat files could more conveniently be kept in a database. Database application example: Using an ATM •A database in the bank keeps data about your account •Passwords are verified to allow transactions to be done on your account •Transactions are recorded in the central database of the bank •Ensures that no two transactions can be done in parallel in a way that create anomalies Database application example: Purchasing from a supermarket •The supermarket database keeps data such as product bar codes, product names, and price. •Products are scanned at the checkout counter and is looked up for the price. •Promotion discount information are also kept. •The database is also used in acquisition of products by the supermarket. Data as a Resource • One of the most vital corporate resources • Used for planning and decision making • Measurement of performance and profitability • Integrated into product design and marketing DATA IS A CORPORATE ASSET Metadata Data that describe the properties or characteristics of other data, it is data about data. Database Management System A general-purpose commercial software system used to define, create, maintain, and provide controlled access to the database. Traditional File Processing Systems • • • • • focused on the needs of individual departments custom development for each application used flat files, usually sequentially accessed reliance on central IS personnel no reuse A file is a collection of related records. Disadvantages of File Processing Systems • • • • • • • Program-data dependence Duplication of data Limited data sharing Lengthy development time Excessive program maintenance No “Overall Map” - single view Application-oriented development The Database Approach Goal The integration and sharing of data throughout the organization Managing Databases Section A File and Database Concepts The term data file has multiple definitions. You can use clues from the context of the sentence it is used in to decide what it means. Data management refers to the tasks associated with maintaining and accessing the data stored in a data file. Each data file has a file structure that describes the way in which the data is stored in that file. Section A File and Database Concepts Section A A file contains records that are made up of fields Fields What is the basic building block for a data file? A field contains the smallest unit of meaningful data and can be thought of as the basic building block for a data file. Each field has a field name that describes its contents. A variable-length field expands to fit the data you enter. A fixed-length field contains a predetermined number of bytes. Data Types Are there any special rules about the data I can enter in a field? The data type specifies the way data is represented on the disk and in RAM. every field in a file is assigned a data type A numeric data type is assigned to fields containing numbers. a real number contains a decimal point an integer is a whole number Data Types Are there any special rules about the data I can enter in a field? A character data type is assigned to fields containing data that does not have to be manipulated mathematically. names, cities, telephone numbers The date data type is used when you want to manipulate dates. The logical data type is used to store true/false or yes/no data. A memo data type is used for entering comments. Records What is the relationship between an entity and a record? An entity is a person, place, thing or event. A record contains fields of data about one entity. Flat Files Do all of the records in a data file contain the same fields? A flat file is sometimes used to refer to a data file in which all records have same field names, field lengths, and data types. single record type used when you want a single file and not a database not efficient for complex data management tasks Flat Files Do all of the records in a data file contain the same fields? Using two flat files to calculate pay requires the computer to work back and forth between the two files. Databases Does a database offer flexibility for using more than one file? A database has many definitions. It is a term that is used loosely. An accurate definition of a database is a variety of different record types that are treated as a single unit. Databases Does a database offer flexibility for using more than one file? When a computer uses related record types from a database to calculate pay, it can combine two records to create a record that contains the data from both files. Databases Does a database offer flexibility for using more than one file? A database has more flexibility than a flat file but is more difficult to design and maintain. A database administrator supervises database design, development, testing, and maintenance. Section B Data Models A data model is a description of the way that data is stored in a database. helps you understand the relationships between entities helps you create efficient structure to hold your data Entity Relationships How does a data model describe data? A relationship is an association between entities. Database designers graphically depict data models using diagramming techniques. Entity Relationships How does a data model describe data? A data diagram can also show cardinality – the number of occurrences that can exist between two record types. Three possible types of cardinality are: one-to-one one-to-many many-to-many Entity Relationships How does a data model describe data? Diagramming cardinality Employee Social Security Card A one-to-one relationship is shown by using a single line to connect the boxes that represent record types. Employee Employee Timecard Job A one-to-many relationship is shown by adding a “crow’s foot” to the end of the line next to the record type with many occurrences. A many-to-many relationship is shown by adding a “crow’s foot” to both ends of the connecting line. Entity Relationships How does a data model describe data? One-to-one relationship = one record of a record type is related to only one record of another record type One-to-many relationship = one record in a record type may be related to more than one record of another record type Many-to-many relationship = one record in a particular record type can be related to many records in another record type and vice versa Entity Relationships How does a data model describe data? Data diagram An Employee has many Timecards. A Job is held by many Employees. Each Department has many Employees. A many-to-many relationship exists between Job and Department.