Relational Database

Database Management System (DBMS)

Database Approach Data definition language (DDL). –Permits specification of data types, structures and any data constraints. –All specifications are stored in the database. Data manipulation language (DML). –General enquiry facility (query language) of the data.

Database Approach Controlled access to database may include: –A security system. –An integrity system. –A concurrency control system. –A recovery control system. –A user-accessible catalog. A view mechanism. –Provides users with only the data they want or need to use.

Views Allows each user to have his or her own view of the database. A view is essentially some subset of the database.

Views Benefits include: –Reduce complexity; –Provide a level of security; –Provide a mechanism to customize the appearance of the database; –Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed.

Practice Open Microsoft Access Open Example database Insert 3 records into the Department table DeptManager Description Marketing Accounting Customer service Create a query to select all department with Dept=“001”

Basics of the Relational Model The relational model represents information in tables (called relations) –Each table represents a set of entities –Each column of a table represents the attribute values of the entities –Each row of a table represents a single entity The rows of a relational table are unique Every table must have a key

Relation Schemas and Keys A key declaration is a constraint –A table is not allowed to have 2 different rows that have the same value for the key –Database systems enforce key constraints By blocking any attempt to modify a table that will result in a violation of the key constraint A relation schema is the specification of the structure of a table –Name of the table –Name and type of each attribute –Declaration of the key

Relational Model Terminology A relation is a table with columns and rows. –Only applies to logical structure of the database, not the physical structure. –Attribute is a named column of a relation. Domain is the set of allowable values for one or more attributes.

Relational Model Terminology Tuple is a row of a relation. Degree is the number of attributes in a relation. Cardinality is the number of tuples in a relation. Relational Database is a collection of normalized relations with distinct relation names.

Instances of Branch and Staff (part) Relations

Examples of Attribute Domains

Alternative Terminology for Relational Model

Properties of Relations Relation name is distinct from all other relation names in relational schema. Each cell of relation contains exactly one atomic (single) value. Each attribute has a distinct name. Values of an attribute are all from the same domain.

Properties of Relations Each tuple is distinct; there are no duplicate tuples. Order of attributes has no significance. Order of tuples has no significance, theoretically.

Practice Inside Microsoft Access, and Example database. Open the table Department (by double click) Repeat the first row of the table Department (creating duplication tuples/record/row)

Relational Keys Primary Key –Candidate key selected to identify tuples uniquely within relation. Alternate Keys –Candidate keys that are not selected to be primary key. Foreign Key –Attribute, or set of attributes, within one relation that matches candidate key of some (possibly same) relation.

Relational Integrity Null –Represents value for an attribute that is currently unknown or not applicable for tuple. –Deals with incomplete or exceptional data. –Represents the absence of a value and is not the same as zero or spaces, which are values.

Relational Integrity Data integrity: state that said the data contained in a database is correct Entity Integrity –In a base relation, no attribute of a primary key can be null. Referential Integrity –If foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null.

Relational Integrity

Enterprise Constraints/User-defined constraints –Additional rules specified by users or database administrators.

Views Base Relation –Named relation corresponding to an entity in conceptual schema, whose tuples are physically stored in database. View –Dynamic result of one or more relational operations operating on base relations to produce another relation.

Relationship types One-to-One relationship: each record is related to only one record in the related table. One-to-Many relationship: each record in a table can have multiple related records Many-to-Many relationship: each record in a table can be related to multiple records in another table and vice versa.

Practice Create a table “Employee” with 3 fields: –SSN: char (11) –Name: char(100) –Salary: double Set SSN as the primary key Select Tools -> Relationships -> Select tables Department -> Add, then Employee -> Add. In the Relationship window, draw a connection from Employee table to Department table

Our Database ISBN Title AuthorID Genre Year PublisherID Pages Price Cover Subject AuthorId Name PublisherId PublisherName Website AuthorBook Publisher UserId Password AddressStreet AddressTown Zipcode TransactionId User TransactionId UserId BookId Date Status Transaction

Projects Project 1 (database) –Part 1: create database, tables, populate data, make links between tables –Part 2: modified existing database, add more tables, links –Part 3: query –Part 4: database front-end (form) –Part 5: advanced forms –Part 6: reports