4+1 View Model of Software Architecture

4+1 View Model of
Software Architecture
Basharat Hussain
23rd Nov. 2016
COMSTAS IIT - WAH

Outline
• Problem
• Solution
• 4+1 view model
• Logical view
• Process view
• Development view
• Physical view
• Use-case view
• The Notations

The Problem
• Arch. documents over-emphasize an aspect of development (i.e.
team organization) or do not address the concerns of all stakeholders.
• The stakeholders of software system:
• end-user,
• developers,
• system engineers,
• project managers
• Software engineers struggled to represent more on one blueprint,
and so architecture documents contains complex diagrams

Different stakeholders – different prospective
• Architecture also means different things to different stakeholders.
• For example,
• a Network Engineer would only be interested in the hardware and network
configuration of the system;
• a Project Manager in the key components to be developed and their
timelines;
• a Developer in classes that make up a component; and
• a Tester in testable scenarios.

Solution
Solution came from “4+1” view model
• The views are used to describe the system from the viewpoint of
different stakeholders, such as end-users, developers and project
managers.
• Suitable for large and challenging architectures
• Describe different aspects of the system into different views.
• (Why?) Because different stakeholders have different aspects
• DEVELOPERS – Aspects of Systems like classes
• SYSTEM ADMINISTRATOR – Deployment, hardware and network configuration
• TESTER , PM, CUSTOMER -- ???
• “4+1” view model provides a “better organization with better separation of
concern”.

4+1 View Model of Software Architecture

4+1 view model architecture
(for distributed systems)
1. Logical View (or Structural View) - an object model of the
design
2. Process View (or Behavioral View) - concurrency and
synchronization aspects
3. Development View (or Implementation View) - static
organization (subset) of the software
4. Physical View (or Deployment View) - mapping of the
software to the hardware
+1. Use-cases View ( or Scenarios) - various usage scenarios

13 UML2.0 diagrams in ‘4+1 View Model’ Architecture

1. Logical View = (The Object-oriented Decomposition)
• Viewer: End-user
• Considers: Functional Requirements- What the system should
provide in terms of services to its users.
• What this view shows?
• “This view shows the components (objects) of the system as well as
their interaction/relationship”.
• Notation: Object and dynamic models
• UML diagrams: Class, Object, State Machine, Composite Structure
diagrams

2. Process View = (The Process Decomposition)
• Viewer: Integrator(s)
• Considers: Non-Functional Requirements - (concurrency, performance,
scalability, usability, resilience, re-use, comprehensibility, economic and
technology constraints, trade-offs, and cross-cutting concerns - like
security and transaction management)
• “This view shows the processes (workflow rules) of the system and how
those processes communicate with each other”.
• UML diagrams: Sequence, Communication, Activity, Timing, Interaction
Overview diagrams

3. Development/Implementation View
= (The Subsystem Decomposition)
• Viewer: Programmers and Software Managers
• Considers: Software module organization (Hierarchy of layers,
software management, reuse, constraints of tools)
• “This view shows the building blocks of the system”.
• UML diagrams: Component, Package diagrams
• Package Details, Execution Environments, Class Libraries, Layers, Sub-system design

4. Physical/Deployment View
= (Software to Hardware Mapping)
• Viewer: System Engineers
• Considers: Non-functional Requirements for hardware
(Topology, Communication)
• “This view shows the system execution environment”.
• UML diagrams: Deployment diagrams
• Non-UML diagrams: Network Topology (not in UML)
Non-functional

5. Use-case View/Scenarios = (putting it altogether)
• Viewer: All users of other views and Evaluators
• Considers: System consistency, validity
• “This view shows the Validation and Illustration of system
completeness. This view is redundant with other views.”.
• UML diagrams: Use-case diagram, User stories

Relationships between Views
• The Logical View and the Process View are at a conceptual level and are
used from analysis to design.
• The Development View and the Deployment View are at the physical level
and represent the actual application components built and deployed.
• The Logical View and the Development View are tied closer to
functionality (functional aspect) . They depict how functionality is modeled
and implemented.
• The Process View and Deployment View realizes the non-functional
aspects using behavioral and physical modeling.
• Use Case View leads to structural elements being analyzed in the Logical
View and implemented in the Development View. The scenarios in the Use
Case View are realized in the Process View and deployed in the Physical
View.

Why is it called the 4 + 1 instead of just 5?
• The Use-case View: The use case view has a special significance.
Views are effectively redundant (i.e. Views are interconnected).
However, all other views would not be possible without use case
view.
It details the high levels requirements of the system.
The other views detail how those requirements are realized.

Correspondence between views
• Views are interconnected.
• They are very close, but the larger the project, the greater the distance.
• Start with Logical view (Req. Doc) and Move to Development or Process
view and then finally go to Physical view.
1. From logical to Process view
 Two strategies to analyze level of concurrency:
 Inside-out: starting from Logical structure
 Outside-in: starting from physical structure
2. From Logical to development view
 Grouping to subsystems is based on:
 Classes
 Class packages
 Line of codes
 Team organization

Software Architecture Definition by IEEE
“Software Architecture is the fundamental organization
of a system, embodied in its components, their
relationships to each other and the environment, and
the principles governing its design and evolution.”
— The definition of Software Architecture as per IEEE Recommended
Practice for Architectural Description of Software Intensive Systems
(IEEE 1471-2000)

Logical View – Notations (functional requirements)
• Class diagrams and class templates are usually used to illustrate the
abstraction. Common mechanisms or services are defined in class
utilities.

Process View – Notations (Non-functional requirements)
• A process is a group of tasks that form an executable unit and which can be (a)
tactically controlled, (b) replicated, (c) partitioned into a set of independent
tasks: major and minor (cyclic activities, buffering, time-outs).

Development/Implementation View - Notation
It consists of libraries and subsystems representation in dev
environment. The subsystems are organized into the hierarchy of
layers with well-defined interfaces.

Development View / Implementation View -
Example

Deployment/Physical View - Notations
Represents non-functional requirements such as availability, reliability,
scalability and performance. It shows how networks, processes, tasks and
objects are mapped onto the various nodes.

A typical Implementation
Model

Deployment/Physical View - Example

Scenarios / Use Case Model (Small PABX)

Enterprise Architecture
• If Solution Architecture is analogy to Building Blueprint, then
Enterprise Architecture will be analogy to City Blueprint.
• The scope of Enterprise Architecture covers the entire enterprise
rather than just 1 business unit.

Definition of Enterprise Architecture
• The MIT Center for Information Systems Research (MIT CISR) in 2007
defined enterprise architecture as:
“Enterprise architecture is the organizing logic for business
processes and IT infrastructure reflecting the integration and
standardization requirements of the company’s operating model. The
operating model is the desired state of business process integration and
business process standardization for delivering goods and services to
customers”.

Sun Tone Cube Architecture (Partitioning)
• The Sun Tone cubic shows a 3 dimensional cube that represent 3
important aspect of technology architecture.
• Tiers: Represent the separation of concern
• Layers: Hardware and Software Stack
• Systemic Qualities: cross functional
requirements of the IT System.

Still - One Size Does Not Fit All
• The architect community hasn’t agreed on a “Unified Architecture
Method”.

This architecture method comprises of the following views:
• Business view : The business view gives the business sponsor’s prospective
on ‘why we are doing it?’ The drivers, goals, context and measurements.
• Functional view : The functional view illustrates a system from a user’s
perspective. It gives answers to the ‘What’ questions: What is the
information, for which users, what are the services and at what qualities.
• Technical view : The application view illustrates a system from a builder’s
perspective and answer the ‘How’ questions: how the system will be
structured, how it will be constructed, how are the constraint handled?
• Implementation view : The infrastructure view depicts the system from a
Deployer’s point-of-view. It answers the ‘With’ questions: With what
product, with whom (people, governance), When/Where (rollout,
deployment).

Each view defines Architecture Principle, Architecture Model and Architecture Standards.
• 1. Architecture Principle: Principles are general rules and guidelines, intended to be enduring and seldom
amended, that inform the way in which an organization sets about fulfilling its mission. For example, if a
person’s principle is to “have integrity”. That will guide his actions and decisions; He would most likely have
a behavior standard not to steal. Therefore architecture principle provides the guidance to architecture
standards that is actionable. (Standard may be more likely subjected to changed than Principle). The format
for Defining Principles is:
• Name: Principle Name
• Statement: Unambiguous statement that communicate the fundamental rule.
• Rationale: Describe why the principle is established.
• Implications: Describe the requirements, both business and IT, for carrying out the principle.
• 2. Model: Diagram that describe the architecture view.
• 3. Architecture Standard: Standards are rules for how to define the structure throughout the
architecture. Taking the same example on ‘Integrity’ principle, the standard may be “When I found a wallet
that does not belongs to me, I will return it to the police station.” Notice that the standard is actionable and
design directly take reference to this standard and must comply with the architecture standard.

A good architecture method should give guidance on how to address
the coherence between architecture views. The HP Global Method
achieves views coherence through Architecture Principles. Architect
first defines the Business Architecture Principle, then derives the
Functional Architecture Principle and followed by Technical and
Implementation Architecture Principles. These principles once
finalized, forms the guiding principles for the definitions of model and
standard in each of its respective view.

4+1 View Model of Software Architecture

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