 DEFINE THE ENTITY  IDENTIFY THE ENTITY TYPES AND SETS OF ENTITY  EXPLAIN THE ATTRIBUTE AND A VALUE SET  EXPLAIN E-R MODEL EXPLAIN THE FOLLOWING RELATIONSHIP TYPES IN E-R MODEL: 1:1(ONE TO ONE) 1:M(ONE TO MANY) M:N(MANY TO MANY)  DRAW E-R MODEL BASED ON A GIVEN SITUATION

 Entity is an object of the real world which can store data and can be defined with clarity.  Example : something that exist physically such as individual, place, article or something that exists conceptually such as an event or concept in a user environment.

ENTITY EXAMPLE invidual Customer, Worker, Supplier venue / place District, State, Country object Stationary, Furniture event Purchase Order, Booking, Sale concept Project, Account, Unit

 Recursive Entity -A recursive entity is one in which a relation can exist between occurrences of the same entity set. This occurs in a unary relationship.  Composite Entity -If a Many to Many relationship exist we must create a bridge entity to convert it into 1 to Many. Bridge entity composed of the primary keys of each of the entities to be connected. The bridge entity is known as a composite entity. A composite entity is represented by a diamond shape with in a rectangle in an ER Diagram.

 Strong Entity Type  Entity type that is not existence-dependent on some other entity type.  Weak Entity Type  Entity type that is existence-dependent on some other entity type.

Entity Set  An entity may be concrete such as a person, book etc or may be abstract such as account,loan etc. The ER model refers to a specific table row as an entity instance or entity occurrence. Collection of similar entities (Entity Set) often corresponds to a table. Each entity set has a key.All entities in an entity set have the same set of attributes. Thus entity set is a set of entities of the same type that share the same properties or attributes. An entity is represented by a rectangle containing the entity name, which is a noun usually written in capital letters.

 A description or an entity characteristic is known as an attribute.  Used to differentiate object in an entity.  The symbol used to represent attribute is oval and connected to entities by lines

 Simple Attribute has only one component, exist independently and cannot be broken up. ( name or gender )  Composite Attribute comprises of many components, each one existing independently. ( address with sub attributes such as house_no, road_no, town, postcode)

 Solitary Valued Attribute is an attribute that consists of only a single value. (matric_no, ic_no )  Multi-Valued Attribute is an attribute consisting of many values. ( telephone no)  Derived Attribute is an attribute where its values is derived from the value of related attributes or set of other attributes. ( age attribute derived from the date of birth )

[ composite attribute ] [ multi-valued attribute] [ derived attribute] [ simple attribute] STUDENT matricno age address dateofbirth gender studentname postcode garden road houseno phoneno specialty

TYPES IN ER MODEL ONE TO ONE ONE TO MANY MANY TO MANY

One to one 1 :1  This type of relationship takes place when a single occurrence of an entity is related to just one  Occurrence of a second entity.  For example, a ROOF covers one BUILDING; a BUILDING is covered by one ROOF.

One-to-many 1:M  Relationships occur when each record in TableA may have many linked records in TableB but each record in TableB may have only one corresponding record in TableA.

EXAMPLE II  In the one-to-many relationship a loan is associated with at most one customer via borrower, a customer is associated with several (including 0) loans via borrower

Many to many M: N  Relationship where multiple rows from table A can correspond to multiple rows in table B.  An example of such a relationship is a school where teachers teach students.  In most schools each teacher can teach multiple students and each student can be taught by multiple teachers.

EXAMPLE II  A customer is associated with several (possibly 0) loans via borrower  A loan is associated with several (possibly 0) customers via borrower

 The relationship type order connects entities chemical and supplier.  The relationship is many-to-many because each chemical can be from several suppliers and each supplier has a number of chemicals.

 An order has a purchase date, amount, and total cost as well as the chemical and supplier information.  Thus, order has attributes PurchaseDate, amount, and TotalCost that we cannot appropriately associate with chemical or supplier.