But there are many technical reasons, mainly because developers don't think like browsers or even users, let alone search engine spiders - they think like programmers. Take the article we mentioned earlier, which appeared on :.exampleomkeyword-xand :.exampleomarticle-categorykeyword-x. If you ask the developers, they'll say it only exists once.
In the eyes of developers, the unique identifier of the article is the ID of the article in the database, not the URL. But for search engines, the URL is the unique identifier of a piece of content.
Session ID
For example, you often want to track visitors and allow them mexico mobile database to place items they want to buy in a shopping cart. In order to do this, you have to give them a "session". A session is a brief history of what the visitor has done on your site, and can include things like items in their shopping cart. In order to maintain that session as the visitor clicks from one page to another, a unique identifier for that session, called a session ID, needs to be stored somewhere. The most common solution is to do this using cookies. However, search engines don't typically store cookies.