Main Concepts:

Enhanced Entity Relationship Diagrams $($EERD$)$:

ii$.$ Completeness Constraint:

Total Specialization Rule $($An instance of the supertype must also belong to either of the

subtypes; Use double line$)$

Partial Specialization Rule $($An instance of an entity could belong to either of the subtypes of

none of them; Use single line$)$

i$.$ Disjointness Constraints:

Disjoint Rule $($Instance of Supertype could be only ONE of the subtypes; write a $"d"$ within circle$)$

Overlap Rule $($Instance of Supertype could be more than one subtype; write an $"$o$"$ within circle$)$

i$.$ Subtype Discriminator $($attribute of the supertype that describes to which subtype an

instance of the entity belongs$)$

If Disjoint: a simple attribute is created with different categories for each subtype

If Overlapping: a composite attribute is created with subparts indicating whether or not an

instance of the entity belongs to each separate subtype$)$

i$.$ Entity Clusters $($If model gets too complex, we can group it into "clusters" by replacing

them with an abstract entity type$)$

ii$.$ Packaged Models $($the search for best practices means that rather than build our

models entirely from the ground up$,$ we can acquire data models from vendors$)$

Universal data model $($generic model template that can be reused with ease in multiple

scenarios$)$

Industry$-$specific data model $($predefined models for specific scenarios$)$

A technology company provides offerings to its customers. Offerings are of two separate types:

products and services. Offerings are identified by an offering ID and an attribute of description. In

addition, products are described by product name, standard price, and date of first release; services

are described by name of the company's unit responsible for the service and conditions of service.

There are repair, maintenance, and other types of services. A repair service has a cost and is the

repair of some product; a maintenance service has an hourly rate. Fortunately, some products never

require repair. However, there are many potential repair services for a product.

A customer may purchase an offering, and the company needs to keep track of when the offering

was purchased and the contact person for that offering with the customer. Unfortunately, not all

offerings are purchased. Customers are identified by customer ID and have descriptive data of name,

address, and phone number.

When a service is performed, that service is billed to some customer. Because some customers

purchase offerings for their clients, a customer may be billed for services he or she did not purchase,

as well as for ones that were purchased. When a customer is billed for a service $($although some may

never require a service of any type$),$ the company needs to keep track of the date the service was

performed, the date the bill is due, and the amount due.

Are there any supertype$/$subtype relationships present? If so$,$ what entities would be involved?

Which would be the supertype, and which would be the subtype?

fill in the blank and fix any error on diagram please