4.1 Logical Architecture in OOAD

Logical Architecture

• Logical architecture is a type of structural design that provides a detailed description of a system without defining its technology or environment.
• It includes information related logically and provides a detailed description without using technical terms.
• It is a diagram used to define the relation between software components.
• The main purpose of designing logical architecture is to plan for the system and use it for communication before designing and implementing the system.
• It provides an overview of the system and is defined as the organization of subsystems, software classes, and layers that make up the complete logical system.
• Components can be deployed in physical computers and operating systems and can be used by the network.
• Logical architecture is created to define the interaction of operations with the system to be understood properly.
• It is represented by a block diagram, which displays the system's operations logically.
• Logical architecture is decomposed into different tiers, including client tier, access tier, presentation tier, business service tier, and data tier.

Layers

• A layer is a specific type of logical architecture that organizes a software system into a series of layers or tiers based on their functionality and responsibilities.
• Each layer provides a set of services to the layer above it and uses services provided by the layer below it.
• This helps to separate concerns, promote modularity, scalability, and maintainability in the system.
• There are various types of layers, including presentation layer, application layer, domain layer, infrastructure layer, and data access layer.
• Each layer has its own responsibilities and interacts with the other layers in a specific way to achieve the system's goals and requirements.
• The use of layering in logical architecture is a common practice in software development and is especially useful for large and complex systems.

Software Architecture

• Software architecture is the highest-level design of a software system, considering multiple perspectives and practical concerns.
• It provides a basic design of a complete software system, defining the elements included in the system, their functions, and how they relate to one another.
• Software architecture considers various factors, including what the system will be used for, who will be using it, and what quality matters to them.
• It is essential for large software systems, providing a solid basis for developers to follow.
• A clear architecture helps to achieve quality in the software, making it easier to maintain, reuse, and adapt.
• Software architecture is useful for various stakeholders, including software developers, project managers, clients, and end-users.
• It provides a collection of several views, including use case view, design view, implementation view, process view, and development view.

UML Package Diagram

• UML Package Diagrams are used to illustrate the logical architecture of the system, including layers, subsystems, and packages.
• Package diagrams are structural diagrams used to show the organization and arrangement of various model elements in the form of packages.
• A package is a grouping of related UML elements, such as diagrams, documents, classes, or even other packages.
• Package diagrams are used to provide a visual organization of the layered architecture within any UML classifier, such as a software system.
• The basic components of a package diagram include packages, dependencies, and packageable elements.

Dependencies

• Dependencies are a visual representation of how one element (or set of elements) depends on or influences another.
• Dependencies are divided into two groups: access and import dependencies.
• There are three types of dependencies: element import, package import, and package merges.
• Element import is a directed relationship between an importing namespace and an imported packageable element.
• Package import is a directed relationship between an importing namespace and an imported package.
• Package merges are directed relationships in which the contents of one package are extended by the contents of another.

Interaction Diagram

• Interaction diagrams are used to capture the interactive behavior of a system, focusing on describing the flow of messages within a system.
• They provide context for one or more lifelines within a system and can be used to represent the ordered sequences within a system.
• Interaction diagrams can be used to model a system as a time-ordered sequence of events, reverse- or forward-engineer a system or process, and organize the structure of various interactive events.
• There are four main types of interaction diagrams in UML: communication diagram, sequence diagram, timing diagram, and interaction overview diagram.

Communication Diagram

• Communication diagrams are used to show the relationship between objects in a system, emphasizing the structural aspects of an interaction diagram.
• They depict the architecture of the objects residing in the system, based on object-oriented programming.
• A communication diagram is also known as a collaboration diagram.
• The notations of a communication diagram include objects, actors, links, and messages.

Sequence Diagram

• Sequence diagrams are a visual representation of interactions between objects or components in a system or program.
• They are commonly used in software development to describe the flow of messages, actions, or events that occur during a specific use case or scenario.
• In a sequence diagram, objects or components are represented as vertical lines, called lifelines, which depict their existence over time.
• Messages or actions between these objects are depicted as horizontal arrows or dotted lines, indicating the order and direction of the interaction.
• The notations of a sequence diagram include lifelines, actors, activation, and messages.### Message Types
• Call Message: represents a communication between lifelines of an interaction, where the target lifeline invokes an operation.
• Return Message: represents the flow of information from the receiver of the corresponding caller message.
• Self Message: describes a communication between the lifelines of an interaction, where a message is invoked within the same lifeline.

Sequence Diagram

• A sequence diagram represents a high-level interaction between objects, showing the sequence of events.
• Example: online bookshop sequence diagram, where an online customer can search for a book, view a description, add a book to their shopping cart, and do checkout.

Class Diagram

• A class diagram describes a static view of an application, showing the types of objects present in the system and their relationships.
• It represents classes, attributes, functions, and relationships to provide an overview of the software system.
• Class diagrams are used to visualize, describe, document, and construct executable software code.
• They consist of class names, attributes, and functions in separate compartments, aiding software development.

Class Diagram Notations

• Class: represented by a rectangle with the class name inside, written in boldface and capitalized.
• Attributes: variables or properties of a class that define its state, listed below the class name and often preceded by a "+" or "-" symbol to indicate public or private visibility.
• Methods: functions or operations of a class that define its behavior, listed below the attributes and often preceded by a "+" or "-" symbol to indicate visibility.
• Inheritance: a relationship between two classes where one class inherits the attributes and methods of another, depicted by an arrow pointing from the subclass to the superclass.
• Association: a relationship between two classes indicating a connection or dependency, depicted by a line connecting the two classes, with optional arrows and multiplicity notations.
• Aggregation: a relationship between two classes where one class contains or is composed of another, depicted by a diamond shape on the container class, with a line connecting it to the component class.
• Composition: a stronger form of aggregation where the part or component cannot exist without the whole or container, depicted by a filled diamond shape on the container class, with a line connecting it to the component class.

Class Diagram Example

• A class diagram can be used to describe a sales order system, showing the classes, attributes, and relationships involved in the system.

Explore the concept of logical architecture and layers in Object-Oriented Analysis and Design (OOAD). Learn how logical architecture provides a detailed structural description of a system without specifying the technology used. Understand the role of logical architecture in defining relationships between software components.