Name the three stages in the process of developing database system .summarize th
ID: 3551250 • Letter: N
Question
Name the three stages in the process of developing database system .summarize the tasks in each?
What is a data model and what is it purpose?
What is a prototype and what is its purpose?
What is a use case, and what is its purpose?
Give an example of a data constraint .?
Give an example of a business rule that would need to be documented in a data base development project?
Define the term entity and give an example other than those used in this book?
Explain the difference between an entity class and an entity instance.?
Define the term attribute and give examples for the entity you described in question 4.7?
Define the term identifier and indicate which attribute defined in your answer to question
4.9 identifies the entity?
Define the term composite identifier and give an example other than those used in this book?
Define the term relationship and give an example other than those used in this book?
Explain the difference between a relationship class and a relationship instance?
Define the term degree of relationship and give an example other than one used in this text of a relationship greater than degree two .?
Define the term maximum cardinality and minimum cardinality ?
Explain the ambiguity in the definition of the term weak entity .explain how this book interprets this term.?
Explanation / Answer
1) Requirements and its analysis: gather requirements by interviewing stakeholders, developing use cases. Analyse the requirements to get the objects, entities.
Design: Use the objects to make class diagram and finally develop the ER Diagram.
Implementation: build database, relations, relationships, populated the database and construct application programs to access the database easily.
2) A data model is a representation of the content, relationships, and constraints of the data needed to support the requirements. It is used to document data
requirements in a way that can be later transformed into a database design.
3) A prototype is a working demonstration of selected portions of a future system. A prototype is an easy way to show elements of the database model design to
users and to get their feedback such that requirements gathered are verified and changed if required. Prototype is developed when requirements are not much clear.
4) A Use Case is a list of steps (functionalities), typically defining interactions between a role and a system, to achieve a goal. In the Use Case diagram, Use Cases
are associated with actors who can be a human or an external system.
5) Example of data constraint: An attribute's value should be of particular type (varchar, number) or say within some limits (by applying check constraint) are
data constraints
6) Say the database is of some bank. Then a business rule can be that the customer account is frozen if a certain balance is outstanding for a certain number of
days.
Business rules are genrally implemented with stored procedures and triggers.
7) Entity is a thing in the real world with an independent existence. It may be object with physical existence (like car, house, employee) or conceptual existence
(like company, job, university course)
eg: Theatre, Movie etc. (some of the examples are in the previous brackets)
8) An entity class is a person, place, event, or thing about which data is collected.An entity instance is an occurence of an entity class. For eg, Student is
an entity class where Will Smith is an entity instance.
9) The particular properties that describe an entity. A particular entity will have value for each of its attributes.
Entity: Theatre
Attributes: TheatreId, TheatreName, Capacity, Owner
10) Identifier is the primary key of the entity. It is the attribute which uniquely determines the records (tuples) of the entity. It should be unique and not null.
In Theatre, TheatreId is the identifier
11) If one attribute is not enough to determine the records of an entity, then we can make more than one attributes as the identifier of the entity records. These
attributes are called composite identifier.
eg: Say a employee works in more than one project for a fixed no. of hours. Then EmployeeId and ProjectNo together will identify the records as EmployeeId will not
be unique in the entity but they together will be unique.
12) Whenever an attribute of one entity type refers to another entity type, a relationship exists. A relationship comprises of more than one entities and in the schema
the relationship is expressed generally through foreign keys.
eg: Movie entity is related to Theatre entity ( relationship name being runs_in ), and the foreign key in Movie will be TheatreId
13) Relationship class defines a set of associations among entities whereas Relationship instance actually associates n individual entities .
14) The degree of relationship is number of participating entities. If no. of participating entities is 2, then it is binary relationship,
and if no. of participating entities is 3, then it is ternary relationship.
eg: ternary relationship: Supply relationshhip between Supplier, Part and Project
15) Maximum cardinality indicates how many instances are participating in a relationship. The possibilities include one-to-one (1:1),
one-to-many (1:M), or many-to-many (M:N).
The minimum cardinality indicates the smallest number of participants in a relationship, which can be 0 or 1 (optional or mandatory).
16) The entity which doesn't have its own identifier( primary key ) is called weak entity. The ambiguity is that taking say more than three attributes will make a
good identifier, but it doesn't suit well. So, we have identifying entity for that entity which should be strong.
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