that4loopgirl

The Unified Modeling Language (UML) is a graphical model used to create specifications for various components of a software system. The parts of UML include:  Class Diagram : similar to E – R diagram  Use case Diagram : shows the interaction between users and the system, and the steps of tasks that user performs.   Activity Diagram : depicts the flow of tasks between various components of the system.  Implementation Diagram : shows the system components (both, software level and hardware level) and their interconnections

The features of the E – R includes specialization, generalization, higher level & lower level entity sets, attribute inheritance, and aggregation. 1. Specialization An entity set may have subgrouping of entities that are different from other entity set in some form. These entity grouping can be represented using E – R model. The process of describing subgrouping within an entity set is known as Specialization . An entity set may be specialized by more than one distinguish feature. For example, consider an entity set named person , having attributes name , street , and city . The person can be classified as: customer or employee . A set of attributes that includes all the attributes of entity person are described by each of these person type. For example, customer entities may be further described by attribute customer_id , and the employee entities can be further described by attributes employee_id, employee_salary. Consider another example, suppose bank decides to d

A weak entity set is an entity set which does not have sufficient attributes to form a primary key. A strong entity set is an entity set with primary key. For example, the entity set payment has three attributes: payment_number, payment_date and payment_amount . Each payment entity is distinct, but payments for different loans may share same payment number. Hence, this entity set does not have a primary key, and it is a weak entity set. A weak entity set must be associated with another entity set, called the owner or identifying entity set . The weak entity set is said to be existence dependent on the identifying entity set. The relationship associating weak entity set with identifying entity set is called identifying relationship. In the above example, the identifying entity set for  payment is loan , and the relationship loan_payment that associates payments and loan entities is an identifying relationship. The discriminator of a weak entity set, also called part