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For example, many dynamic web sites employ query string parameters that generate different URLs

that host very similar or identical content. This is interpreted as

duplicate content

by search engines,

and this can get the pages penalized. The use of many URL parameters may also result in

spider traps

(

http://en.wikipedia.org/wiki/Spider_trap

), or in linking structures that are hard to follow

by a search engine. Needless to say, both scenarios reduce the web site’s ranking performance with the

search engines. Duplicate content is discussed in Chapter 5.

Because the web developers reading this book are architecting dynamic sites, these subjects must be

examined in depth. And we start by categorizing URLs into two groups based on their anatomy:

?

Static URLs

?

Dynamic URLs

Static URLs

Static URLs

do

not

include a query string. By this definition, a URL referencing a PHP script

without

parameters is still static. Two examples of static URLs are as follows:

http://www.example.com/about-us.html

http://www.example.com/site-map.php

Static URLs — even those generated by a PHP script — typically pose no challenges for a search engine.

Dynamic URLs

Dynamic URLs

are those that include a query string, set off by

?

, a question mark. This string is used to

pass various parameters to a PHP script. Multiple parameters are delimited by

&

and then appended to

the query string. A typical dynamic URL looks like the following:

http://www.example.com/product.php

?category_id=1&product_id=2

In this example,

product.php

is the name of a physical file containing a PHP script on a web server.

The highlighted section is the query string. When a web browser makes a request to the PHP script with

a particular query string, the script may then present differing content based on the various parameters.

However, the script does not necessarily have to present different content based on different permuta-

tions of the query string — which is the basis of the most common cause of duplicate content. The most

trivial example of this is when you add a parameter that does not change the presented content at all,

such as in these examples:

http://www.example.com/product.php?product_id=2&extra_param=123

http://www.example.com/product.php?product_id=2&another_extra_param=456

Because the query string values affect the script’s output, a search engine typically con-

siders the same file name with differing query strings as completely different web

pages, despite the fact that those pages originate from the same physical script file.

39

Chapter 3: Provocative SE-Friendly URLs

c03.qxd:c03 10:39 39

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