I concur with Carlos Cebruán, you should read the NIST document. SaaS for me includes both the ability to run the service and the concepts of scalability, eventual multi-tenancy and of the business component (billing, SLAs, etc.). A Web Service is just a technological mechanism to implement a software capability. A service may be exposed as a web service, but just being a web service does not make something an example of SaaS.

Gokulnath, does you have read the "The NIST Definition of Cloud Computing" document. If not, I suggest you to do it: it'll clarify better than me the 5 essential (let me say "mandatory") features that any service must have to be condisered as Cloud Computing (doesn't forget that SaaS mis one of the 3 Service Models: IaaS, PaaS and SaaS)

I concur with Carlos Cebruán, you should read the NIST document. SaaS for me includes both the ability to run the service and the concepts of scalability, eventual multi-tenancy and of the business component (billing, SLAs, etc.). A Web Service is just a technological mechanism to implement a software capability. A service may be exposed as a web service, but just being a web service does not make something an example of SaaS.

The NIST document we cited is at: http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf

Just to add some examples..

SaaS - Google Docs

Web Service - What most all of the Tablet / Phones 'APPS' use to get the data.. Think of the twitter app that shows up on any devices.. It uses the Web Services provided by Twitter to read the data.

SaaS in very simple terms is a complete application, while Web Services is one of the method that can be used to build a complete application

SaaS is a mature application (or even a set of services) that provides utility to some group of users (as an overused example, think Salesforce.com) whereas a web service tends to be some specific functionality (i.e., calculation tool, data query), often part of a larger suite of services (e.g., broad set of calculations, or big data access). I think it is a matter of scale---with a web service being a subset, more of than not, than SaaS. Of course, there are exceptions within any of the comparisons.

On additional thing I would add is that web services will often provide only the data being offered by the service (usually in XML format). The consumer either needs to obtain (or create) an app to visualize the data in a human friendly way. You can also often display web services data in an excel spreadsheet using the WSDL as a style guide.

We should realize that we are confusing "web services" in the meaning of a programming technique/methodology (as Wolf Tomb uses) and a Service offered by a provider(e.g. a company) ot its users (e.g. human customers) avaliable (accesible) in the company's web (also Web Service). I think the latter is the one Golkunath asked about, not the former, but Golkunath should clarify this in order to could focus the discussion.

Another point, Gokulnath, let me suggest to read my old post (2012-may-29) in http://wp.me/p2cqZY-d4: it's about "Real” Cloud Computing Services vs. “Fake” Cloud Computing Services

SaaS (Software as a Service) is a series of software provided by the Cloud Company when you are on the Cloud while web services are the normal online services you get when you are connected to the internet. Although SaaS also requires the internet to function.

Uchechukwu,

You are using a very interesting definition of "web services" as those being any service obtained from any website. As Carlos correctly points out, industry as defined a somewhat different meaning commonly associated with the term "web services" which is to generally imply a Service Oriented Architecture (SOA) based fine grained service available from the web commonly via a SOAP over HTTP protocol request.. This does not mean your use of the term is not appropriate; only that it is not typically what a lot of technologists would consider without further definition.

Given the further detail you provide I would offer this: Software as a Service often implies subscribing to software capability which historically could be provided "in-house" in companies and even by a individual that wants to purchase the necessary equipment and software to do so themselves. A good example, would be email. Traditionally, most companies hosted their own servers running an email software package (exchange, Louts notes, or any number of their email software applications). I myself, run my own home based server, on which I have installed an email "post office" software called "Smart Mail". I maintain this in my basement and use it to receive and send mail within my the domain I own for my home email use. However, today many individuals and companies subscribe to online email such as Gmail, Hotmail, Yahoo mail etc. These are considered "Software as a Service" because people are consuming the "service" of the email software package via the cloud (web) without needing to by the software package and run it themselves.

This gets a little confusing when considering "other services" received from general websites. The services from these sites are not necessarily based on a single "traditional" software package and one that a user cold purchase and install themselves (either in their company) or at home if they wanted to invest in the equipment, network connection and software of they wanted to. An example might be news media websites which provide users with daily news about events of the day. Given your definition the web service here would be providing the ability o stay informed and up to date with what is happen in your community and around the world. But, there is no readily available software package you could purchase to provide this on your own.

I hope this helps explains the difference a little bit.

As stated by Paulo Melo, the NIST document at:

http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf

gives briefly different types of services such as

Software as a Service(SaaS)..

Platform as a Service(PaaS)

Infrastructure as a Service(IaaS).

and different types of Deployment models like

Private cloud

Community cloud.

Public cloud

Hybrid cloud

Saas is one of the Services Provided by Cloud Computing.through any one of the Deployment Models.

The cloud Model is accessed through Web Service.

The clouds are located int different Servers located at different places by different cloud Model Providers.

Defining Cloud SLAs Is Critical as Posted by Esther Shein April 30, 2012

http://www.networkcomputing.com/cloud-computing/defining-cloud-slas-is-critical/232901139

Service level agreements(SLAs) have been used by companies for a long time in an effort to ensure they get the right bang for their buck, but industry experts say that with IT functions increasingly being moved to the cloud, it’s important to carefully define your goals in SLAs so that corners are not cut in an effort to increase the provider’s bottom line.

SLAs written with cloud providers must remain "specific, measurable, achievable, relevant and timely," and "should leave no ambiguity as to what both service providers and service consumers expect,"’ says Frederick Rose, service assurance practice director at Fusion PPT,

Earlier, Wolt Tombe has further Qualified Web Service as follows.

As Carlos correctly points out, industry has defined a somewhat different meaning commonly associated with the term "web services" which is to generally imply a Service Oriented Architecture (SOA) based fine grained service available from the web commonly via a SOAP(Simple Object Access Protocol,) over HTTP protocol request.. This does not mean your use of the term is not appropriate; only that it is not typically what a lot of technologists would consider without further definition.

P.S.

.

I fully agree with Pisupati: a good summary in all the sujjects

SaaS is software as service, using which you accomplish the task/work you assigned it for. Webservice is a service through which you can port data from legacy system to SaaS. Hope this helps

Shall we conclude that

SaaS = Web Service + scalability + portability + billing + SLA's +.....

Simply NO

How about... web service = API, SaaS = application -- assuming that application depends on APIs to be implemented. Simplistic yes, but easy to understand.

Cloud computing finding its root in SOA. All services used in cloud are webservices of any category SOAP,JSON or REST.