What is exactly achieved by Semantic web?

The web is currently filled with documents. There are reams of English text that can be consumed only by humans. Blogs like this add to the ever increasing pile of text content. Of course there are also other types of content like photos, images, videos and so on. Thus the web is increasingly becoming a way of  publishing content mainly for human consumption. The interesting aspect of these documents are they are linked to one another meaningfully enabling a user to traverse those hyper links and read all the linked content. For example, I point here the link to the W3C Semantic Web project W3C Semantic Web. Thus there is no need to repeat what one has already published and instead

All this is good and we could have lived like this happily.  Then came Tim Berners Lee, the original inventor of the web. He saw that the web of documents is having a large amount of data that includes not just fancy content, but dates and numbers and text and currencies and you name it. It appeared like if we could process this data, we can gain insight into a treasure trove of data that is on the public web. 

Now to achieve this, the web pages should be published with additional information or the semantics or the meaning of what is there in the content of a page. This meaning or semantics could be seen as tags that extend the existing information of the content of a web page. For example, there could be a string in the page which tells the name of the author of this web blog as 'Thalapathy'. There could be other things that can be tagged to denote the date on the page as the date on which the blog was written. There could be tags that denote the comments on the web blog, the dates and so on. And there can be tags that tell that the page is about 'Semantic Web'. Thus there can be innumerable pieces of data within a page that denotes a lot more additional semantics that a program can query on.

If we make parallels to the database world, this is about looking at the whole web as one large database.  

Query can be done the way a SQL is done on relational tables. This allows connecting disparate data across the web across several web pages to be able to answer a question. For example, the fact that a event reported in Bangalore on a Semantic Web conference can be related to a book released in California and its popularity from customer reviews in Amazon can be connected because the author who wrote that book attended the conference and the book is sold on Amazon which in turn gives the reviews on it. This is not something that can be achieved with a simple Google search. It requires data to be related across seemingly disparate pieces of knowledge. 

Thus Semantic Web opens up a whole lot of possibilities in humans and machines on behalf of them being able to see the web as a extended human consciousness offering answers to what otherwise would have looked an impossibility.