QUESTION:
a.Identify Entities, their attributes, and relationships among the entities for the given scenarios and present in a preliminary ER-Diagram.
b. Identify all existing Super key, candidate key, primary key, foreign key, composite key, derived key and partial key for any one entity type of each scenario.
SCENARIO:
A local car dealer has contracted you to design a database system that will track car repairs made by its technicians. In the system design, a mechanic must be assigned to each car for repair as each repair is tracked via a work report. Moreover, the database system should be able to generate a report for the customer that contains a description of the work that was performed, date, time, and result.
Answers
Answer:
Explanation:
An Entity–relationship model (ER model) describes the structure of a database with the help of a diagram, which is known as Entity Relationship Diagram (ER Diagram). An ER model is a design or blueprint of a database that can later be implemented as a database. The main components of E-R model are: entity set and relationship set.
An ER diagram shows the relationship among entity sets. An entity set is a group of similar entities and these entities can have attributes. In terms of DBMS, an entity is a table or attribute of a table in database, so by showing relationship among tables and their attributes, ER diagram shows the complete logical structure of a database. Lets have a look at a simple ER diagram to understand this concept.
KEYS in DBMS is an attribute or set of attributes which helps you to identify a row(tuple) in a relation(table). They allow you to find the relation between two tables. Keys help you uniquely identify a row in a table by a combination of one or more columns in that table. Key is also helpful for finding unique record or row from the table. Database key is also helpful for finding unique record or row from the table.