Database

DatabaseDatabase

Basic Definitions

• Database: A collection of related data.• Database Management System (DBMS):

A software package/ system to facilitate the creation and maintenance of a computerized database.

• Database System: The DBMS software together with the data itself. Sometimes, the applications are also included. ( Software + Database )

Relational Database

Data Models

• High Level or Conceptual data models provide concepts that are close to the way many users perceive data, entities, attributes and relationships. (Ex. ERD)

• Physical data models describes how data is stored in the computer and the access path needed to access and search for data.

Entity Relationship Diagram Entity Relationship Diagram [ERD][ERD]

Entity Relationship Modeling

• Entity-Relationship Diagram (ERD): Identifies information required by the business by displaying the relevant entities and the relationships between them.

Entity Relationship Modeling, (Cont.)

• In building a data model a number of questions must be addressed:– What entities need to be described in the

model?– What characteristics or attributes of those

entities need to be recorded?– Can an attribute or a set of attributes be

identified that will uniquely identify one specific occurrence of an entity?

– What associations or relationships exist between entities?

Entity

• An entity is a thing that exists and is distinguishable -- an object, something in the environment.

• Examples : book, item, student• Types of entities:

– Regular entity (Strong entity): if its existence does not depend on another entity.

– Weak entity: if its existence depends on another entity.

Attribute

• An entity has a set of attributes• Attribute defines property of an entity• It is given a name• Attribute has value for each entity and value

may change over time• Example : BOOK entity has the following

attributes (TITLE, ISBN, AUTHOR, PUBLISHER, YEAR, PRICE)

Attribute Types

• Simple: Each entity has a single atomic value for the attribute ; e.g., SSN

• Composite: The attribute may be composed of several components ; e.g., Name (FirstName, MiddleName, LastName)

• Multi-valued: The attribute may has more than one value for a given entity; e.g., a book may have many authors

• Derived attributes: The attributes whose values are generated from other attributes using calculations ; e.g., Age is derived by subtracting current date from birthdate

• Primary Key: an attribute of an entity type for which each entity must have a unique value; e.g., SSN of EMPLOYEE.

• Composite key: e.g., ID is a key of the applicant entity type with components (National_ID, Application_no)

• Foreign Key (referential attributes): Attributes that define relationships between entities. The attributes of a foreign key in one entity are the attributes of a primary key in another entity; e.g., Department ID is the primary key of Department and Department ID is a foreign key of Employee defining the relationship "Employee works for Department"

Key Attribute

Relationships

• Relationships: A relationship is a connection between entity classes.

• The cardinality of a relationship indicates the number of instances in entity class E1 that can or must be associated with instances in entity class E2.– One-One Relationship: (citizen – passport , – One-Many Relationship: (student-Advisor,

Customer-Order)– Many- Many Relationship: (e.g. Student-

Organization, Order-Products)– Recursive Relationships: A relationship in which

the same entity participates more than once.

• Binary relationship: between two entity sets– e.g., binary relationship set STUDY between

STUDENT and COURSE• Ternary relationship: among three entity sets

– e.g., ternary relationship STUDY could be ternary among STUDENT, COURSE and TEACHER

– A relationship may have attributese.g., attribute GRADE and SEMESTER for STUDY

Relationships, (cont.)

Optional And Mandatory

Optional And Mandatory, (cont.)

ERD Notations

• Rectangles represent ENTITY CLASSES

• Circles represent ATTRIBUTES • Diamonds represent RELATIONSHIPS • Arcs connect entities to

relationships. Arcs are also used to connect attributes to entities. Some styles of entity-relationship diagrams use arrows and double arrows to indicate the one and the many in relationships.

• Underline - Key attributes of entities are underlined.

Summary Of ERD Notations

Example

Add Some Attributes To Entities

Exercise

• A company is organized into departments. Each department has a unique name, a unique number, and a particular employee who manages the department.

• A department may have several locations.• A department may control a number of projects,

each of which has a unique name, a unique number, and a single location.

• A project must controlled by department.• We store employee’s name, social security number,

address, salary, gender and birth date.

• An employee must be assigned to one department and must work on one or more projects, which are not necessarily controlled by the same department.

• We keep track of the number of hours per week that an employee works on each project.

• We also keep track of the direct supervisor of each employee.

• We want to keep track of the dependents of each employee for insurance purposes.

• We keep each dependent’s first name, gender, birth date and relationship to that employee.

Exercise, (cont.)

ERD Mapping to TablesERD Mapping to Tables

ER-to-Relational Mapping

• Step 1: Mapping of Regular Entity Types• Step 2: Mapping of Weak Entity Types• Step 3: Mapping of Binary 1:1 Relation Types• Step 4: Mapping of Binary 1:N Relationship

Types.• Step 5: Mapping of Binary M:N Relationship

Types.• Step 6: Mapping of Multi-valued attributes.• Step 7: Mapping of N-ary Relationship Types.• Step 8: Map recursive Relationship Types

Step 1: Mapping of Regular Entity Types

• Create table for each regular (strong) entity type.

• Choose one of key attributes to be the primary key.

Step 2: Mapping of Weak Entity Types

• Create table for each weak entity.• Add foreign key that correspond to the

owner entity type.• Choose the primary key : ( FK + weak entity

Partial PK if any).

Step 3: Mapping of Binary 1:1 Relation Types

1. Merged two tables if both sides are Mandatory.

2. Add FK into table with the Mandatory relationship to represent optional side.

3. Create a third table with just the keys from the two tables in addition to the two table if both sides are optional.

Step 4: Mapping of Binary 1:N Relationship Types

• If the N-side is mandatory, add FK to N-side tableAdd any simple attributes of relationship as column to N-side table.

• If the N-side is optional, create a third tableThe of the new table consists of a concatenation of the keys of the related entities. Include any attributes that were in the relationship.

Step 5: Mapping of Binary M:N Relationship Types

• Create a new third table• Add FKs to the new table for both parent

tables• Add simple attributes of relationship to the

new table if any .

Step 6: Mapping of Multi-valued attributes

• Create new table for each multi-valued attribute

• Table will include two columns: one for multi-valued attribute + FK column.

Step 7: Mapping of N-ary Relationship Types

• If n > 2 then :• Create a new third table• Add FKs to the new table for all parent

tables• Add simple attributes of relationship to the

new table if any .

Mapping of N-ary Relationship (Example)

Step 8: Map recursive Relationship Types

• For recursive entities, two types of mapping rules have been developed:

• 1:N recursive relationships, re include the primary key of the table with the recursive relationship in the same table, giving the key some other name.



• For M:N recursive relationships, create a separate table for the relationship

Referential Integrity

• Referential Integrity requires that:– The columns of a foreign key must match in type

the columns of the primary key in the referenced table.

– The values of the foreign key columns in each row of the referencing table must match the values of the corresponding primary key columns for a row in the referenced table.

37

Referential Integrity, (cont.)

38

• No Action– only primary keys with no matching foreign keys can be

deleted/Updated– the change to the referenced (primary key) table is not

performed.

• Cascadewhere the foreign key in the case matching is deleted/updated.– For update (the primary key column values have been

modified), the corresponding foreign key columns for referencing rows are set to the new values.

– For delete (the primary key row is deleted), the referencing rows (foreign key) are deleted


39

• SET NULL– All matching foreign keys are set to null, and

delete/update then takes place in other relation.

• SET Default– all matching foreign keys are set to default value, and

delete/update then takes place in other relation.


40

Mapping Result

Thank YouThank You

Documents

Database