Question

Tim is a small car repair shop owner. The customer either drops in or makes an appointment for car repair. For basic services, Tim charges a fixed amount. For major repair, he first performs inspection, charges the customer for inspection, and then on customer consent repairs the car. He then allows the customer either for full payment or monthly payment, depending on the amount of repair. The supplies are ordered or reordered as and when required.

Physical ERD design and needs to align with the following guidelines:

1. Your physical ERD conceptual model needs to include all the correct relationships between the entities (i.e., one to many, many to many).
2. You need to include all the correct entities, but you don’t need to include the attributes for each entity.
3. Your model needs to use Crow's Foot Notation.

Answer 1

Crow’s Foot Notation:-

A number of data modeling techniques are being used today. One of the most common is the entity relationship diagram (ERD). Several ERD notations are available.

Components used in the creation of an ERD:-

Entity – A person, place or thing about which we want to collect and store multiple instances of data. It has a name, which is a noun, and attributes which describe the data we are interested in storing. It also has an identifier, which uniquely identifies one instance of an entity. The attribute which acts as the identifier is marked with an asterisk.

Relationship – Illustrates an association between two entities. It has a name which is a verb. It also has cardinality and modality.

Cardinality and Modality are the indicators of the business rules around a relationship. Cardinality refers to the maximum number of times an instance in one entity can be associated with instances in the related entity. Modality refers to the minimum number of times an instance in one entity can be associated with an instance in the related entity.

Cardinality can be 1 or Many and the symbol is placed on the outside ends of the relationship line, closest to the entity, Modality can be 1 or 0 and the symbol is placed on the inside, next to the cardinality symbol. For a cardinality of 1 a straight line is drawn. For a cardinality of Many a foot with three toes is drawn. For a modality of 1 a straight line is drawn. For a modality of 0 a circle is drawn.

Cardinality and modality are indicated at both ends of the relationship line. Once this has been done, the relationships are read as being 1 to 1 (1:1), 1 to many (1:M), or many to many (M:M).

Typically, ERDs are much more complex than this, involving quite a number of entities and relationships. If we join all of the above relationships together and add a few attributes, a small collection of data might be depicted in the following way using Crow’s Foot Notation: