Software as a Service

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How hardware industry differs from software industry?

Hardware industries are been established for centuries and they are the major assets of the country. After software industries have been established software and hardware integrated projects have been in peek for the growth of technological and social well being. After both sectors grown well all eyes goes to the difference imposed by both sectors and question arises what drives an industry. This post is meant for explanation regarding software but it doesnt mean that sofware is more important.

Hardware

• Harware designs are to be finished before manufacture otherwise it would lead to a great disaster wasting all the resources and if finds default then whole harware has to be replaced. Also the quality of the hardware diminishes with time and the cost of upgrade seems to be infinitely.

Software

• Software evolves over time to integrate new functionalities and new features.When there is a bug then the new version can be released,it only matters for few line of code to be replaced.

There are two kinds of softwares

Legacy software are those which satisfies users needs but difficult to evolve due to design inelegance or antiquated technology.Currently, 60% of s/w maintenance cost is used for adding new functionality to the legacy s/w and only 17% for bug fixing.

Beautiful software meets customer needs and are easy to evolve.

There are different approaches for s/w development.
First one is Waterfall model. The levels in waterfall model are:

1. Requirement specification
   
2. Design
   
3. Construction(implementation or coding)
   
4. Integration
   
5. Testing and debugging
   
6. Installation
   
7. Maintenance
   

The main drawback of this model is that, when the customer is unclear or less specific about the requirements, the developed model mail fail to meet the goals.
The second one is Spiral model. In this model, a prototype is built in every phase discussed above and then developed in each phase.

1. Determine the objectives, alternatives, and constraints on the new iteration.
2. Evaluate alternatives and identify and resolve risk issues.
3. Develop and verify the product for this iteration.
4. Plan the next iteration.

This also helps in back tracking, reversing or revising the process.

The third is Agile model. The key features of this model are:

• Embraces change as a fact of life: continuous improvement vs. phases.
• Developers continuously refine working but incomplete prototype until customers happy, with customer feedback on each iteration (every ~2 weeks).
• Agile emphasizes Test-Driven Development (TDD) to reduce mistakes, written down User Stories to validate customer requirements, Velocity to measure progress.
  

Testing and Formal methods

Testing cannot be exhausting. Testing has many levels:

• The base thing is called unit testing. That's testing to see if a single method does what's expected.
• The next level is module or functional testing to test across individual units, like with across classes versus within a class.
• Integration testing is to try and see if a bunch of modules communicate correctly. It's a more narrow interface., and each time when we add one of these things, we're assuming the one below does that work.
• Finally, at the top is system or acceptance testing, tests weather the whole program meet what the customer wants it to do.

Types of Testing:

1. Coverage testing specifies the percentage of code paths that have been tested.
2. Regression testing is used to automatically rerun old tests to ensure that the current version still works at least as well as it used to.
3. Continuous integration testing, which means the entire program is tested every time new code is checked in, versus later phases.

Software as a Service (SaaS)
Software as a Service (SaaS) delivers software and data as a service over the Internet, usually via a thin program such as a browser that runs on local client devices instead of binary code that must be installed and runs wholly on that device. Eg: searching, social networking, and videos.

Service oriented Architecture(SOA)

SOA defines how to integrate widely disparate applications for a Web-based environment and uses multiple implementation platforms. Rather than defining an API, SOA defines the interface in terms of protocols and functionality. An endpoint is the entry point for such a SOA implementation. SaaS is a special case of a software architecture where all components are designed to be services. SOA actually means that components of an application act as interoperable services, and can be used independently and recombined in other applications.The contrasting implementation is considered a 'software silo', which rarely has APIs to internal components.
SaaS has 3 demands on infrastructure,

• Communication- Allow customers to interact with the services.
• Scalability- Fluctuations in demand during new services to add users rapidly.
• Dependability- Service and communication available at any time.

The critical distinction of SOA is that no service can name or access another service’s data; it can only make requests for data through an external API.
Collections of commodity small-scale computers connected by commodity Ethernet switches- clusters, offeres scalable and much cheaper serving.The public cloud services or utility computing offers computing, storage, and communication at pennies per hour.
In order to efficiently use a SOA, the architecture must meet the following requirements:

• Interoperability among different systems and programming languages that provides the basis for integration between applications on different platforms through a communication protocol. One example of such communication depends on the concept of messages.
• Desire to create a federation of resources. Establish and maintain data flow to a federated database system. This allows new functionality developed to reference a common business format for each data element.
  

Cloud Computing
Cloud computing is the use of computing resources (hardware and software) that are delivered as a service over a network (typically the Internet).Cloud Computing provides the scalable and dependable hardware computation and storage for SaaS. Cloud computing consists of clusters of commodity servers that are connected by local area network switches, with a software layer providing sufficient redundancy to make this cost-effective hardware dependable.