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11 May 2009

RUP – Software Component Architecture

Filed under: RUP,UML — Tags: , , , — admin @ 09:11

What is Architecture?

  • In computer science, Architecture is the nature and structure of a system that determines the way it operates.

What Architecture is not:

  • Architecture is not a Framework: While an architecture can take into account the use of a framework, the definition of a framework is not sufficient! A framework is just one component.

The Technical Architecture (or Model of Architecture) is the nature of the system. For instance, it could be:

  • Monolitic
  • Client Server
  • Distributed
  • N-tier

Paradigms can be integrated, such as:

  • Model-View-Controller
  • Software Components
  • Design patterns

A framework can be defined, as part of the technical architecture.

The business architecture defines the structure of the system.
It should outline the different parts of the system, their role and their relationships, as for instance:

What Does Component Architecture Mean for RUP?

  • Components are cohesive groups of code, in source or executable form, with well-defined interfaces and behaviours that provide strong encapsulation of their contents, and are therefore replaceable.
  • Architectures based around components tend to reduce the effective size and complexity of the solution, and so are more robust and resilient.
  • In the examples below, there is the same number of objects, but a different level of complexity:

Definition for Software Component

  • A Software Component is an independent portion of code that is accessed through a defined interface.
  • Software Components may be just imaginary, and can always be defined whatever the technology used!
  • Software Components may also be physical entities, such as a library (e.g. DLL) or a distributed component (e.g. EJB, CORBA, DCOM, Web Services, etc.)… but not necessarily… and it is not because EJB are used that it is a well-thought Software Component Architecture.
  • Physical Software Components may be reused, purchased and/or replaced.

Business components are those that implement the functionality specific to a business.
A “Computation Engine”, which provides specific computation services, is an example of a business component.
Business components are more difficult to reuse than technical components, due to their specific nature.

Technical components are those that implement generic functionality.
An example of a technical component is “Document Printing”.
Technical components can be designed in order to be reused. They can be part of a technical framework.

Why using Software Components?

  • They usually manage to reduce the complexity of a software, by identifying well defined interfaces and independent portions of code.
  • While it is rather inefficient to give Use Cases to develop to Programmers directly, it is much more effective to give components to implement. ==> Would you envisage to outsource the development of a use case? It is easy to outsource the development of a component, or to buy an existing one.
  • This approach eases and improves workload estimations, planning & task assignment.
  • To reuse components is an efficient way because they are already developed and tested.

Components can be developed in order to be reusable, especially the components that provide common solutions to a wide range of common problems.
These reusable components, which may be larger than just collections of utilities or class libraries, form the basis of reuse within an organization, increasing overall software productivity and quality.
Before promoting furious reusability however, ensure that great experience and knowledge has been acquired in the domain of software components.

Because they are well defined, Components can be refactored with less pain than in a not-so-well structured / organised Architecture.
The interface of the component may be mostly unchanged, while the implementation is entirely reviewed.
Even if the interface is changed, finding the impacted code will be easier than finding what is using the multiple classes and methods that compose the component.

In the beginning of Software Development, documentation and system integration were usually poorly undertook, the Architect was often asked to contribute to the development effort, and the Customer would get to perform most of the testing.

RUP recommends to implement “Use Case Packages” as components for requirements, in order to gather requirements by type of functionality.
Indeed this approach will ease the following analysis and design of the application with software components.

Identifying components may be performed this way:

  • Identify different modules, packages, subsystems and layers, e.g. Billing and Subscription modules.
  • Try to find common features, e.g. printing out.
  • Split modules, define interfaces and relationships with other modules.
  • Iterate and go deeper to find as many components as possible. Use top-down approach, from Graphical Interface towards Data, and bottom-up approach at the same time.
  • Then apply patterns such as Model-View-Controller.

The Components specification will provide a brief description of the components and their relationships.
The result is usually described with Composite Structure or Component Diagrams and accompanying text, providing a high-level description for each component.

The Components Analysis will provide a brief definition of each component, and a detailed definition of its interfaces and relationships.
At this stage, Components are black boxes.
The result is usually obtained and described with Sequence Diagrams and/or Collaboration Diagrams. Class Diagrams can be used to describe the interfaces.

The Components Design will provide the detailed description of what is inside each component / inside the box.
The result is usually obtained and described with Sequence Diagrams, Collaboration Diagrams, Class Diagrams, State Diagrams, etc.

The implementation of the components can now easily be performed by a Developer or a Team.
The team will be responsible for maintaining the design of the component and for unit testing the component.
The team might be the supplier and/or the customer for another component/team.

Components can be individually tested and gradually integrated to form the whole system.When performing unit tests of a component, moke components (giving fake answers) can be used to form the test-bench of the component to test.

Note also that Service Oriented Architectures (SOA) are necessarily based on Software Components Architectures. Components are then implemented as services (Web-services, CORBA, RMI, etc.), which provide the benefit of being loosely coupled.

9 May 2009

Risk Analysis 101

Filed under: Project Management,RUP — Tags: — admin @ 09:33

In my experience, Risk Analysis is primarily about communication. If the communication going around the project is not open and efficient, no risk analysis approach will save it.
On the other hand, if there is good communication going, a simple risk analysis methodology will do wonders.

The objective of a risk analysis is to identify, quantify and as much as possible mitigate the effects of events that have the potential to prevent a project from reaching its objectives. A risk analysis is not about identifying dysfunctions or people to blame.

The goals of a risk analysis is to:

  • give confidence to the Project Manager that all the contingencies have been considered
  • help working teams to focus on the key issues
  • mitigate the potiential impact of certain risks
  • help to prepare for the unexpected
  • improve the control over the development life-cycle and increase the capability to achieve the project objectives

A common method consists in brainstorming sessions, which allow to establish a list of risks. Each risk has an assignee, who will have the responsibility to help analysing the risk, usually the subject matter expert.
Let’s remind ourselves now one fundamental principle of risk analysis: “No idea is too stupide to be mentionned”. This is why small risks and very important risks will be listed side by side.
Then each risk is the object of a detailled analysis, which will allow to determine the value of a number of attributes. In particular, risks are classified by category.

The following categories may be considered for Software Development projects:

  • Requirements
  • Analysis and Design
  • Coding
  • Test
  • Deployment
  • Training and Documentation
  • Maintenance and Support
  • General

Each risk is also allocated a value for importance. The calculation of the importance is realised by using a Probability-Impact matrix. In the following example the matrix give more importance to the impact over the probability:





Probability \ Severity Low Medium High
Low 1 3 5
Medium 2 6 8
High 4 7 9

Still in the context of the calculation of the importance, it is recommended to undertake a ponderation of the severities in relation to cost, quality and planning, in order to take into account the imperatives of the project.

A risk analysis will allow to highlight a number of solutions susceptible to mitigate the risks. Solutions will translate into actions. Some of these actions will need to be undertaken rapidely, in order to prevent the apparition of risks. They are preventive actions. Some will rely on the risk being triggered. They are curative actions.
Each action is allocated a value for importance too, which is calculated with the importance of risks it is mitigating.

Risks may later be managed using Risk Management Plan type document, or project traking type document, such as Status Assessment.

The source of information should also be documented, as context for the risk analysis. For example, list the brainstorming sessions that have happened and the attendees.

When documenting the results of the risk analysis, it is recommended to provide first the catalog of risks as a summary, sorted by importance. Then describe the risks in details by category.
The following attributes are to be documented for each risk:

  • Description – what it is about
  • Indicator – how do we find out
  • Impact (source part, impacted part, probability, impact severity on cost, quality and planning)
  • Possible solutions – refering to actions

The risk repartition may be documented using charts as for example:

  • Severity repartition for planning, quality and/or cost
  • Risks repartition by category (risks number and % importance)
  • Risks control repartition (risks per person, team, group and/or organisation)

Proposed actions are listed with a reference, a description, an undertaking mechanism and associated risks (which are mitigated by the action).

In conclusion, most of the proposed actions should be preventive and therefore undertaken as soon as possible, as a fundamental principle of risks analysis consists in anticipating problems. Indeed risk analysis is not supposed to provide solutions to existing problems, as it is considered to be late.
It is recommended to undertake a process analyse, as per the RUP methodology for example, in order to describe actions in details and to anchor them within a well known methodology.

Finally the risks analysis identifies New risks. The risks management consists in turning risks from New to Open when they are triggered, and turning them from Open to Closed when they have been treated.

Existing problems, at the time of the risks analysis, aren’t identified as risks, since no probability can associated, but they may be managed as open risks during risk management.

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