ASP.NET System design 2

Unified Modeling Language
(UML)

Background
 What are object-oriented (OO) methods?
OO methods provide a set of techniques for analyzing, decomposing, and
modularizing software system architectures
In general, OO methods are characterized by structuring the system
architecture on the basis of its objects (and classes of objects) rather than the
actions it performs
 What are the benefits of OO?
OO enhances key software quality factors of a system and its constituent
components
 What is the rationale for using OO?
In general, systems evolve and functionality changes, but objects and classes
tend to remain stable over time
Using Object Oriented Design Approach the development team creates the
abstractions and mechanisms necessary to meet the system's behavioral
requirements determined during analysis

Modeling
 Modeling is a way of thinking about the problems using models
organized around the real world ideas.
 A modeling method comprises a language and also a procedure
for using the language to construct models.
 Modeling is the only way to visualize your design and check it
against requirements before your crew starts to code.
 An important reason behind constructing a model is that it helps
manage complexity. Once the models of a system have been
constructed, these can be used for a variety of purposes during
software development, including the following:
 Analysis
 Specification
 Design
 Code generation
 Visualize and understand the problem and the working of a system
 Testing etc

What is UML?
• Is a language. It is not simply a notation for drawing diagrams, but a
complete language for capturing knowledge about a system and
expressing knowledge(syntax) regarding the system for the purpose of
communication and visualizing, constructing and documenting software
system.
• Applies to modeling and systems. Modeling involves a focus on
understanding a subject (system) and capturing and being able to
communicated in this knowledge.
• It is the result of unifying the information systems and technology
industry’s best engineering practices (principals, techniques, methods and
tools).
• The UML uses mostly graphical notations to express the OO analysis and
design of software projects.
• Help acquire an overall view of a system. UML is not dependent on any
one language or technology.

UML View
UML is a multi-diagrammatic language to capture different views of the system.
Structural view-The structural view defines the structure of the problem in
terms of the kinds of objects (classes) important to the understanding of the
working of a system and to its implementation. It also captures the relationships
among the classes (objects). The structural model is also called the static model,
since the structure of a system does not change with time.
Behavioral view-The behavioral view captures how objects interact with
each other to realize the system behavior. The system behavior captures the
dynamic behavior of the system.
Implementation view-This view captures the important components of
the system and their dependencies.
Environmental view-This view models how the different components are
implemented on different pieces of hardware.
Users' view- This view defines the functionalities (facilities) made available
by the system to its users.

UML View, Diagram
Structural View
-Class Diagram
-Object Diagram
Behavioral View
-Sequence Diagram
-Collaboration Diagram
-State Chart Diagram
-Activity Diagram
Implementation Diagram
-Component Diagram
Environmental View
-Deployment Diagram
User’s View
Use Case
Diagram
Theusers'viewcanbeconsideredasthecentralviewandallotherviewsareexpectedtoconform
tothisview.Thisthinkingisinfacttheheartofanyuser-centricdevelopmentstyle.

Use case Diagram represent the different ways in which a system can be used by
users. The Use case diagram is used to identify the primary elements and
processes that form the system. The primary elements are termed as "actors" and
the processes are called "use cases." The Use case diagram shows which actors
interact with each use case. These diagrams contain the following components:
• Actors: An actor or external agent, lies outside the system model, but interacts
with it in some way. An actor may be a user, a representative group of users,
machine, or an information system. Actors are drawn as stick figures with the
name of the actor written bellow of stick figure. Each actor can participate in one
or more use cases.
• Use Cases: The use case diagram for any system consists of a set of "use cases".
Intuitively, use cases represent the different ways in which the users can use a
system. A simple way to find all the use cases of a system is to ask the question:
"What the users can do using the system?" Thus for the Library Information
System (LIS), the use cases could be: issue-book, query-book, return-book etc.
Each use case is represented by an ellipse.
Use case diagrams

Symbols Of Use Case Diagram
Actor
Symbol:
<<actor>>
When a stick person icon
represents an external
system, it is annotated by
the stereotype <<external
system>>
Use Case
Symbol:
Name of the use case is
written inside the
ellipse.
Use Case Name

Relationships in Use Cases
 Include: Literally speaking, in an include relationship; a use case includes the
functionality described in another use case as a part of its business process flow.
 An include relationship is depicted with a directed arrow. The tip of the
arrowhead points to the parent use case and the child use case is connected at
the base of the arrow. The type "<<includes>>" identifies the relationship as an
include relationship.
<<include>>
 Example: “Rent Item” use case executes by a staff in a store “Pay Fee” and
“Check Overdue” also executes.
<<include>>
<<include>>

Relationships in Use Cases
 Extend: In an extend relationship between two use cases, the child use case adds to
the existing functionality and characteristics of the parent use case. The main idea
behind the ‘extends’ relationship among use cases is that it allows to show optional
behavior.
 An extend relationship is depicted with a directed arrow having a dotted shaft, similar
to the include relationship. The tip of the arrowhead points to the parent use case and
the child use case is connected at the base of the arrow.
<<extend>>
 An example of an extend relationship between the "Perform medical tests" (parent) and
"Perform Pathological Tests" (child) use cases. The "Perform Pathological Tests" use
case enhances the functionality of the "Perform medical tests" use case.
<<extend>>

A Simple Use Case Diagram On Railway
Reservation System

Class Diagrams
 Class Diagrams describe the static structure of a system, or how it is
structured rather than how it behaves.
 By definition, a class diagram is a diagram showing a collection of
classes and interfaces, along with the relationships among classes and
interfaces.
 The use cases talk about "what are the requirements" of a system. The
aim of designing classes is to convert this "what" to a "how" for each
requirement. A class diagram is a pictorial representation of the
detailed system design. A thing to remember is that a class diagram is a
static view of a system. The structure of a system is represented using
class diagrams.

Elements of a Class Diagram
The classes represent entities with common features, i.e. attributes and operations. Classes
are represented as solid outline rectangles with compartments. Classes have a mandatory
name compartment. Classes have optional attributes and operations compartments.
Attributes-An attribute is a named property of a class. It represents the kind of data that
an object might contain. Attributes are listed with their names, and may optionally contain
specification of their type – separated by a colon with attribute name, an initial value, and
constraints.
Operation-The parameters of a function may have a kind specified. The kind may be "in"
indicating that the parameter is passed into the operation, or "out" indicating that the
parameter is only returned from the operation, or "inout" indicating that the parameter is used
for passing data into the operation and getting result from the operation. The default is "in".
An operation may have a return type consisting of a single return type expression, for
example, issueBook (in bookName):Boolean

Elements of a Class Diagram[contd..]
 Modifiers are used to indicate visibility of attributes and operations.
 ‘+’ is used to denote Public visibility (everyone)
 ‘#’ is used to denote Protected visibility (derived)
 ‘-’ is used to denote Private visibility (no one)
 By default, attributes are hidden and operations are visible
 For example:
 Here Account is the class name which has three attributes customer_name(type char,
visibility private), account_no( type int, visibility private), balance(type int,
visibility private) and Account class operates addfunds and withdraw method.
Visibility of operations are public.
Account
-customer_name: char
-account_no: int
-balance: int
+addfunds(in amount)
+withdraw(in amount)

Relationship between Classes
 Association -An Association is a generic relationship between two classes, and is
modeled by a solid line connecting the two classes. Associations are needed to enable
objects to communicate with each other.
 A label, which is optional, although highly recommended, is typically one or two words
describe the association. Label is shown alongside association line. A filled triangle
indicates the direction in which the label should be read.
 works for
 An arrow may be attached to the end of the path to indicate that navigation is
supported in the direction of the class pointed to. To restrict the navigation one
direction only an arrowhead is used to indicate the navigational direction.
 In following figure, the association is navigable in only one direction, from
BankAccount to Person, but not the reverse. The Person class is frozen and cannot be
extended to know about the BankAccount class, but the reverse is not true.

Relationship between Classes [contd..]
 On each side of the association relation the multiplicity is noted as an
individual number or as a value range. The multiplicity indicates how
many instances of one class are associated with the other. Value ranges of
multiplicity are noted by specifying the minimum and maximum value,
separated by two dots. An asterisk is used as a wild card and means many
(zero or more).
 The association of above figure should be read as "Many books may be
borrowed by a Library Member”
 0..1 Borrowed by 0..*

 Aggregation -When a class is formed as a collection of other classes, it is
called an aggregation relationship between these classes. It is also called a
"has a" relationship. (It is a special type of association where the involved
classes are not only associated to each other, but a whole- part relationship
exists between them.)
 Aggregation is represented by the diamond symbol at the composite/aggregate
end of a relationship. The number of instances of the component class
aggregated can also be shown in diagram.
1..* consist of 1..* 1..* consist of 1..*
 A document can be considered as an aggregation of paragraphs. Each
paragraph can in turn be considered as aggregation of lines.

 Composition- Composition is a stricter form of aggregation, in which the parts
may belong to only one whole and are existence-dependent on the whole. This
means that the life of each part is closely tied to the life of the whole. In other
words, the lifeline of the whole and the part are identical. When the whole is
created, the parts are created and when the whole is destroyed, the parts are
destroyed. In composition instance of one object contains instances of some
other objects.
 A typical example of composition is an invoice object with invoice items. As
soon as the invoice object is created, all the invoice items in it are created and as
soon as the invoice object is destroyed, all invoice items in it are also destroyed.
The composition relationship is represented as a filled diamond drawn at the
composite-end.
 1 *

 Inheritance/Generalization-Also called an "is a" or “is a kind of “
relationship, because the child class is a type of the parent class.
Generalization is the basic type of relationship used to define reusable
elements in the class diagram. Literally, the child classes "inherit" the
common functionality defined in the parent class.
The inheritance relationship is represented by means of an arrow with empty
triangular arrow head pointing from the subclass to the super-class.

Steps Followed
 Draw class symbol in the and name it
 List the class attributes and try to understand their
visibility
 List the class operations/methods and try to understand
their visibility
 Make the proper links/association and note multiplicity
properly
 Display relationships (if any) between classes.
 Give notations.

Example- A Class Diagram to represent the fact that an order consists of one
or more order items. Each order item contains the name of the item, its
quantity and the date by which it is required. Each order item is described by
an item order specification object having details such as its vendor addresses,
its unit price, and manufacturer.

Object Diagram
 Object diagram is an instance of class diagram. This type of diagram is used
to describe the system at a particular point in time. Using this technique,
designer can validating the class diagram and its multiplicity rules with real-
world data, and record test scenarios. From a notation standpoint, Object
diagrams borrow elements from Class diagrams.
 Object Diagrams describe the static structure of a system at a particular time.
Whereas a class model describes all possible situations, an object model
describes a particular situation. Object Diagram has following two elements:
 Object- Objects, which represent particular entities. These are instances of
classes. Objects are identified by placing the instance name followed by a
colon (:) in front of the class name. Property values are written as
"name=value" pairs. The icon for an object is a rectangle divided into
sections.
 Association- Object diagrams can contain associations as well. Associations
between Objects are simply diagrammed using a line joining the two.

Another Example Of Object Diagram

Sequence Diagram
 The invocation of methods in each object, and the order in which the invocation
occurs is captured in a Sequence diagram. This makes the Sequence diagram a
very useful tool to easily represent the dynamic behavior of a system.
 Sequence Diagrams describe interactions among classes. These interactions are modeled
as exchange of messages. These diagrams focus on classes and the messages they
exchange to accomplish some desired behavior. Sequence diagrams are a type of
interaction diagrams. Sequence diagrams contain the following elements:
• Class roles, which represent roles that objects may play within the interaction.
• Lifelines, which represent the existence of an object over a period of time.
• Activations, which represent the time during which an object is performing an operation.
• Messages, which represent communication between objects.

Sequence diagram for "Manage course information"

ASP.NET System design 2

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