Three-Tier Architecture

23 Questions

A ______ is an entity without a key attribute.

Weak Entity

In ER diagrams, ______ are displayed in ovals.

Attributes

A ______ attribute is displayed in a double oval.

Multivalued

Each ______ attribute is underlined in ER diagrams.

key

A ______ attribute is displayed in a dotted oval.

Derived

The degree of a ______ type is the number of participating entities in a relationship.

relationship

A ______ relationship exists between the instances of the same entity type.

Unary

A ______ relationship exists among the instances of three entity types.

Ternary

An _______________ server runs application programs and stores business rules (constraints).

application

Entities are specific persons, places, events, objects in the user environment about which the user needs to keep _______________.

data

Attributes are properties used to describe an _______________.

entity

A specific entity will have a value for each of its _______________.

attributes

Each attribute has a _______________ type associated with it – e.g. integer, string, …

data

A _______________ relates two or more distinct entities with a specific meaning.

relationship

The _______________ server accepts requests from the client, processes it, and sends DB queries and commands to the DB server.

intermediate

Clients contain _______________ interfaces and Web browsers.

user

EMPLOYEE John Smith works on the PROJECT, or EMPLOYEE Franklin Wong manages the Research .

ProductX, DEPARTMENT

Each attribute has a single ______ value. For example, SSN or Sex.

atomic

The attribute may be composed of several ______ components. For example, Address(Apt#, House#, Street, City, State, ZipCode, Country).

components

An attribute that may have ______ values. For example, Color of a CAR – {Black, White}.

multiple

An attribute that have only a single ______. For example, SSN or Sex.

value

An Attribute with a value ______ by the user to be stored in the DB. For example, BirthDate, Salary, Bonus.

entered

An attribute with a value ______ from other stored attributes and no need to ask user for it. For example, from BirthDate attribute we derive the Age.

derived

Study Notes

Types of Attributes

Simple attribute: has a single atomic value, e.g. SSN or Sex
Composite attribute: composed of several components, e.g. Address (Apt#, House#, Street, City, State, ZipCode, Country) or Name (FirstName, MiddleName, LastName)
Composition may form a hierarchy where some components are themselves composite

Types of Attributes (2)

Single-valued attribute: has only a single value, e.g. SSN or Sex
Multi-valued attribute: may have multiple values, e.g. Color of a CAR – {Black, White} or PreviousDegrees of a STUDENT—{BSc, MSc, PhD}

Types of Attributes (3)

Stored attribute: an attribute with a value entered by the user to be stored in the DB, e.g. BirthDate, Salary, Bonus
Derived attribute: an attribute with a value derived from other stored attributes, e.g. Age from BirthDate or NetSalary from Salary and Bonus

Types of Attributes (4)

Complex attribute: considered composite and multivalued at the same time, e.g. PhoneNumber (country code, gov.code, phone) with multiple values

Entities and Attributes

Entity: a specific person, place, event, or object in the user environment, e.g. EMPLOYEE, Office, Task, Conference
Attribute: a property used to describe an entity, e.g. EMPLOYEE attributes: Name, SSN, Address, Sex, BirthDate
Each attribute has a data type associated with it, e.g. integer, string, …

Relationships

A relationship relates two or more distinct entities with a specific meaning, e.g. EMPLOYEE John Smith works on the ProductX PROJECT, or EMPLOYEE Franklin Wong manages the Research DEPARTMENT
Degree of a relationship type: the number of participating entities in a relationship, e.g. Unary, Binary, Ternary

Types of Relationships

Unary relationship: a relationship between instances of the same entity type, e.g. a person lives with another
Binary relationship: a relationship between instances of two entity types, e.g. EMPLOYEE and DEPARTMENT
Ternary relationship: a relationship among instances of three entity types, e.g. EMPLOYEE, PROJECT, and DEPARTMENT

ER Diagrams

Entities: displayed in rectangular boxes, with weak entities displayed in double rectangular boxes
Attributes: displayed in ovals, with each attribute connected to its entity type
Components of composite attributes: connected to the oval representing the composite attribute
Key attributes: underlined
Multivalued attributes: displayed in double ovals
Derived attributes: displayed in dotted ovals

Three-Tier and n-Tier Architectures

Three-Tier Architecture: improves DB security by checking a client's credentials before forwarding a request to the DB server
N-Tier Architecture: divides the layers between the user and the stored data further into finer components

This quiz covers the basics of three-tier architecture, including the role of application servers, web servers, and database servers in processing client requests and enforcing security constraints.

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