Web 2.0 Overview
Web 2.0 does not have a boundary, it has been compared by O’Reilly  to a solar system. We could consider the concept as the Sun and its services as the planets that are tied to it and that have a different relation between each other and the core (concept). As it happens with the solar system, the most challenging aspect is to understand the diversity of the objects in it and to understand that in the most fundamental sense they are all part of the same family and therefore share a common genetic inheritance [Lewis, 1981]. In the same way Web 2.0 services are different but they all share the same principles and practices. They come from the same origin. Like the solar system, Web 2.0 services have relations between them just as planets do.
Key principles behind Web 2.0
There are several key principles behind the Web 2.0 concept that have been discussed on the initial Web Conference held in 2004 and that authors other than O’Reilly et al. are discussing between themselves. Web 2.0 has three main building blocks behind it: platform, collectiveness and data.
1) Web as a Platform This concept is considered to be Tim O’Reilly strategic positioning on the definition of Web 2.0. We can consider the web as being another layer on top of the traditional computer layers, is the new operating system which is graphic just like Mac OS or Windows is, we can consider it to be our new interface with the computer in which we have different Web 2.0 services., “ In the end, both web browsers and web servers turned out to be commodities, and value moved “up the stack” to services delivered over the web platform” [O’Reilly, 2005].
This desktop concept is known as the “Webtop” and it is a trend that the borderline between the internet and the PC is fading, this is why the main internet and SW companies such as Yahoo!, Google or Microsoft are offereing tools that allow users to personalize the web interface as if it was an operating system [Gomero, 2006]. The net has replaced the PC as the platform that matters, just as the PC replaced the mainframe and minicomputer [Tim O’Reilly]. As Negroponte  states, “Nowadays big changes in IT and telecom come from the applications and basic human needs”, this is how a new desktop that is ubiquous, connected and embracing a social interaction has been created. Just like the O.S. interface made the PC HW a commodity, ubiquity is making both HW and O.S. interface a commodity.
2) Services instead of Applications Web 2.0 is more about services rather than about applications and the SW programs are conceived more as services rather than products [Gomero, 2006]. These services are all social services in the sense that they are built around user data and create relations and communities between users. They are mash ups of different applications that are joined together independently; they are connected between each other and interact dynamically. The bottom line is that SW is delivered as a service instead of as a product [O’Reilly, 2005].This is why it is independent of the device where it is delivered. It is no longer “tied to the PC platform” [O’Reilly, 2005].
These services are continuously being updated so we never really have a closed version: it is the eternal β stage. SW gets better the more it is used [Reilly, 2005] it does no longer get modified and updated every 2 years, it is constantly updated [Gomero, 2006] by the usage and the service it provides.
3) Collectiveness It is about harnessing collective intelligence and creating an open source environment in which an architecture of participation appears and users gain control over the Web. Network effects created by this architecture start happening, all data sources can be mixed or changed by users. Collectiveness intelligence is used to create Web 2.0 services. A new concept appears, “social media” which is the content that is created by users [Gomero, 2006]. According to wikipedia “Access to consumer-generated content facilitated by Web 2.0 brings the web closer to Tim Berners-Lee's original concept of the web as a democratic, personal, and do it yourself medium of communications.”
When a company opens its databases to users, as Amazon, Google, and eBay have done with their Web services, it encourages participation at new levels. “he corporation's data becomes “part of the commons” and an invitation to participate. People who take advantage of these capabilities become the company's developers [Kelly, 2005] they are gaining control over the service and shaping it. As Tim O’Reilly  states: “Leverage customer-self service and algorithmic data management to reach out the entire web, to the edges and not just the center, to the long tail and not just the head”. An example of this is Amazon, where almost 1/3 of its on-line book sales come from non-popular books that are usually not available on traditional stores [Gomero, 2006]. As Anderson  states, “the traditional line between producers and consumers has blurred. Consumers are also producers.” Consumers are now co-creators of services and technological expertise is no longer a barrier to produce web pages.
The fact that there is so much scattered content available posted by users is creating a new equation for the supply and demand model: the long tail. This model states that a big number of items (offer) in the tail multiplied by a relatively small number (demand) is still equal to a big number [Anderson, 2006] which is only getting bigger as the Web 2.0 community which means that demand will start increasing more rapidly and so will the offer.
Data and its management are crucial as the heart of Web 2.0. This is why all successful internet applications have been backed by a specialized database: Google, Yahoo!, Amazon, eBay, Napster. Data base management is a core competency, according to Tim O’Reilly, “The value of the SW is proportional to the scale and dynamism of the data it helps to manage.” A new software concept is emerging, infoware” [O’Reilly, 2005]. The data are dominating Web 2.0 and it is becoming like the “Intel inside” cliché, the better the data quality and the way it is managed, the better the service will be.
Since services are based on data, there is a big volume of it in the Web 2.0 which needs to be managed. This is an artificial intelligence challenge; in order to manage data, tags are used to help categorization and searching for others to discover [Cavanaugh, 2002]. This is what is commonly known as Folksonomy: “a style of collaborative categorization of sites using freely chosen keywords which are referred to as tags” [O’Reilly, 2005]. Further evolution of tagging is the Semantic Web in which data is tagged in a way that it can be understood by machines also, although this subject does have some relation to the Web 2.0 but seen from a different perspective and thus it will not be included in the scope of this document.
Key drivers that enable web 2.0
There are some factors that drive the existence of Web 2.0 according to O’Reilly and Gomero [2004-6]:
•Evolution of software tools for data management that help content classification and discovery.
•High speed access to the internet that allows users retrieve high volume of information rapidly.
•Pervasive access to Internet anywhere any time.
•Internet applications open nature in which the user is the producer.
•Similarity with desktop of Internet services make them easy to use.
•HW price decrease provides master devices with more storage capacity for Server applications.
•Ease of maintenance since content is updated by users. The key driver behind Web2.0 has been the evolution of technology’s presence in people’s lives.
•Evolution of the Web user who has shifted his/her behavior from passive user to active user, hw/she is now in control. Users like to contribute, participate and be part of the Web.
•New social needs driven by IT, Telecommunications and Media convergence. People are now experts on using technology tools such as their PC, their mobile device and the TV and are now expecting more services that allow them to be connected and to be part of a social community that share the same interests.
•Maturity of the Web as a technology product in a way that it needed to “re-invent” itself in order to continue to attract users and grow