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Introduction to Database CSC 240 (Blum) 1 Data versus Information • When people distinguish between data and information, – Data is simply a set of individual numbers or facts. – Information arises from integration – putting the individual facts together to see the larger picture or by asking a question not answerable by just one piece of data. CSC 240 (Blum) 2 Data vs. Information Example • Example of Data: – John Smith got a 87 on Test 2 in CSC 240. • Examples of Information: – John Smith scored more than 10 points over the class average on all of the tests in CSC 240. – Jane Jones got the highest score on Test 2 is CSC 240. CSC 240 (Blum) 3 Database • The purpose of a database is to bring together a set of data so that it is centralized, organized, easy to extract information from, and so forth. • The way the facts are organized and how they relate to each other is known as the database design. • The software application that facilitates the storing of the data and the accessing of the information is known as a database management system. CSC 240 (Blum) 4 Database Modeling • In database design, one tries to organize the data in a way that reflects the situation from which the data comes. • One approach is known as entityrelationship modeling or ER modeling. • The design is often represented pictorially in an ER Diagram. CSC 240 (Blum) 5 Entities • Entities separate the data into distinct units. – E.g. a Person entity collects together individual pieces of data (known as attributes) about a person – Name, Address, PhoneNumber, etc. • Database entities often reflect real objects/entities (persons, buildings, courses, etc.) • An entity is somewhat similar to an object in programming, it collects data that belongs together in some immediate way. CSC 240 (Blum) 6 Relationship • The various entities may be distinct, but they are not completely disconnected. An association between two entities is known as a relationship. – In a database modeling a university, one would have relationships, such as • Student takes class • Professor teaches class • Etc. CSC 240 (Blum) 7 ER Diagram • One can visualize the entities and their relationship using an Entity-Relationship (ER) diagram. – The entities are represented by rectangles. – The relationships are represented by arrows between the rectangles. • The arrow may include a verb to capture the nature of the relationship (as well as other notations). CSC 240 (Blum) 8 CSC 240 (Blum) 9 Design Implementation • After a database is designed, one uses a database management system to implement (actually make) the database. • In database implementation, one encounters terms like table, record, field, keys, and so forth. CSC 240 (Blum) 10 Webopedia definition of record • “In database management systems, a complete set of information. Records are composed of fields, each of which contains one item of information. A set of records constitutes a file. For example, a personnel file might contain records that have three fields: a name field, an address field, and a phone number field. In relational database management systems, records are called tuples.” CSC 240 (Blum) 11 Whatis definition of table • “In a relational database, a table (sometimes called a file) organizes the information about a single topic into rows and columns. For example, a database for a business would typically contain a table for customer information, which would store customers' account numbers, addresses, phone numbers, and so on as a series of columns. • Each single piece of data (such as the account number) is a field in the table. A column consists of all the entries in a single field, such as the telephone numbers of all the customers. • Fields, in turn, are organized as records, which are complete sets of information (such as the set of information about a particular customer), each of which comprises a row. The process of normalization determines how data will be most effectively organized into tables.” CSC 240 (Blum) 12 CSC 240 (Blum) 13 Fields • The lower-level pieces of data gathered together to form an entity are known as fields or attributes or properties. – Thus in our example the Person entity consists of fields like FirstName, LastName, Address and PhoneNumber, etc. • Fields are analogous to properties of an object. • Like properties, they have a type (Text, Number, Yes/No, Memo, Date/Time, etc.) which indicate how the information is to be stored and interpreted. CSC 240 (Blum) 14 Webopedia definition of the key • “In database management systems, a key is a field that you use to sort data. It can also be called a key field, sort key, index, or key word. For example, if you sort records by age, then the age field is a key. • Most database management systems allow you to have more than one key so that you can sort records in different ways. • One of the keys is designated the primary key, and must hold a unique value for each record. • A key field that identifies records in a different table is called a foreign key.” CSC 240 (Blum) 15 References • Database Systems: Design, Implementation, & Management, Peter Rob and Carlos Coronel • http://www.whatis.com • http://www.webopedia.com CSC 240 (Blum) 16