CS 474 Database Design and Application Terminology Jan 11, 2000

Administrivia u Show of hands - who has not had CS239 or ISAT 340 or CS274.

Database u Database - Collection of related data with implicit meaning. Your cards are a database. The phone book is a database. Your filing systems are databases.

Data u Data - Known facts that can be recorded and have meaning. Your cards are the database and what you have recorded (written) on them is the data. The entries in the phone book are data. The information written in your file system is data.

Databases, cont u Collection of related records with specific meanings Random assortment of data is not a database. Designed for a specific purpose. Have a source for the data. Have a specific audience who will use the data. Represents some aspect of the real world. –models real world entities and real world processes.

Database Management System u Abbreviated DBMS. u Collection of programs to enable users to build and maintain databases. u General purpose software, like a programming language.

Database Management Systems, cont u Your book talks about a database system as being a “computerized record-keeping system”. Databases do not need to be on computers, but they do keep records. u Our focus in class will be (of course) the computerized database system.

What makes up a database? u Database - central file store. u File - a collection of individual records. u Record - is a collection of data elements about one entity. u Data element - a single piece of data with properties.

Operations on Databases u Creation and removal of files u Insertion and deletion of individual records within files. u Changing data within existing files. u Retrieving data from existing files.

Database system components u Data u Hardware on which it resides u Software that manipulates the data u Users that maintain or use the data

Data u In a database, data are organized in such a way that we can make efficient use of the data. (Files in a cabinet are organized to make insertion, deletion, and retrieval easier). u The book talks about integretation of data and sharing.

Integration u Separate diverse data (files) are organized in such a way that we can make use of disparate data across the system. For example, if I am in the Admissions office and I want to know which of my recruits from last year are still in school, I would access the Registration information. Integration leads to efficiency of operations.

Integration u Also means that we can reduce the redundancy of the data. If both the Admissions office and the Registrar’s office need names of students, we can store the names in one file and both offices can use those names with their individual files.

Redundancy u This property allows us to control the redundancy in the system, by allowing us to put common data in one place which is accessible from everywhere in the system. u Redundancy - duplication of data across systems.

Why is redundancy bad? u Loss of efficiency - as each office is collecting data, each person is spending time gathering data that the organization already has in hand. u Inconsistency - a change in data in one place is not necessarily propogated to all offices. u Storage is wasted - extra space to house the duplicate information.

Shared data u By integrating the database, you permit your users to share data across offices. u That enables queries, research and processes to use the entire collection of data.

Is all data shared? u Typically, no. u Each user will have his/her own view of the data. That view will be customized to their needs. u Some data should not be viewed by all users. Protections (security) prevent unauthorized access to data.

Hardware u Hardware provides the “file cabinet” for the database. It provides a place on which the data resides. u Hardware also provides us with some tools to maintain the data (keyboard, tapes, modem, memory).

Software - DBMS u The Database Management System (DBMS) provides a layer between the stored data and the users. u All requests for manipulation of data go through the DBMS.

Services typically provided u Design the database. Includes ability to build new files, remove files, add elements to files, establish the “connections” between files. u Manipulate the database. Includes features that enable users to directly access the data housed in the database. Provides change, retrieval, insertion, and deletion functions.

Services provided, cont. u DBMS typically provide a way to protect the data from unauthorized use. Identification of users and password protection of the database level. u DBMS typically provide a way to customize users views of the database (which is also a protection).

Examples of DBMS systems u MS Access u Oracle u MS SQL Server u Dbase Each product from each vendor will have some of its own unique features.

Users u Users provide the fourth component of the system. u Users interpret the data found in the dbms. u Users maintain the database and data within the data base.

User “classes” u Application programmers u End users u Database Administrators

Application programmers u Make use of the database in their programs. u They may issue queries, provide screens, provide reports, provide other processing to the users of the system. u Build “user” interfaces into the application. u Database provides “data independence” with their applications. (Database can change, while applications remain constant).

End Users u Typically use the database through some user interface functions provided by the application programmers. u May use functions provided directly by the database management system, such as queries.

Database Administrator u Maintains the database itself. u Usually maintains the security within the system. u May not decide what the security schema is. u May not decide what is needed in the database.

Databases, cont u Book talks about “persistent” data. Typically a database is developed to retain data over time. u Some of that data will have a longer life than other data. Some data will “persist” for only a few moments to support some other type of processing.

Data as an Organizational Asset u We spend time on databases since data is one of the most valuable assets within an organization. u We spend time collecting it; we spend time retrieving it. u A good database design facilitates the use of that organizational asset. A bad database design will devalue the asset.

Advantages of a database u Data independence - separate the application from the details of the underlying data. Applications interact with the DBMS not with the actual data. u Database applications provide transaction support. A transaction (or logical unit of work) either goes all the way through or goes none of the way. It cannot be divided.

How do we represent that data?

Entities and Relationships u An entity is any object about which we want to gather information. Students Courses Grades Professors u A relationship describes how those entities are connected to one another. (A relationship might be an entity in its own right.)

E/R Diagram u Provides the “picture” of the database using entities and the relationships among those entities. u Take a look at page 11 of the book. u We will spend more time on this shortly.

Entities, cont u Entities have properties which describe that entity. u Your cards have listed some properties of the students that you interviewed. u Each type of entity will have its own unique properties and often some properties that it shares with other entities. Ex. Cars and trucks might be two entities, but they share many properties such as having wheels.

What is a relational database u Any database that is based on the formal theory called “The relational model of data.” u Consists of “tables” which are equivalent to files. u Consists of “rows” and “columns”. u Consists of formal operations to work with the tables.

What are some other types? u Hierarchical database system - Data is represented as a tree structure with pointers from one entity to another. u Netword database system - Data is represented as a network of entities. u The database system is categorized by its data structure. u We will only be dealing with relational databases.

Conclusion u Next time - read chapter 2. We will start on 3 by the end of next week. u Be able to answer exercises in Chap 1.