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consistency also makes it easier to exclude files in

robots.txt

, because the preceding problems having

to do with ordering and casing also apply there.

For example, if you’re building an e-commerce web site, you could create a function such as the following:

function create_link($category_id, $product_id)

{

return ‘product.php?category_id=’ . $category_id . ‘&product_id=’ . $product_id;

}

Calling this function providing

5

and

6

as parameters, it will return

product.php?category_

id=5&product_id=6

. Using this function throughout the web site will ensure all your links follow

a consistent format.

This implementation of

create_link()

is overly simplistic and not really useful for real-world scenarios.

If you want to improve your URLs more significantly, you need to utilize more advanced functions in

coordination with URL rewriting. The benefits of URL consistency will also apply there. So without

further ado, the next section discusses this subject.

URL Rewriting

Taking into consideration the guidelines and recommendations mentioned earlier, this section presents

solutions you can apply in your web applications to accomplish URL-rewriting using the mod_rewrite

Apache module.

The hurdle you must overcome when implementing the URLs shown earlier is that they don’t actually

exist anywhere in your web site. Your site still contains a script — named, say,

product.php

— which

expects to receive parameters through the query string and generate content depending on those param-

eters. This script would be ready to handle a request such as this:

http://seophp.example.com/product.php?product_id=123

But your web server would normally generate a 404 error if you tried any of the following:

http://seophp.example.com/Products/123.html

http://seophp.example.com/my-super-product.html

URL rewriting allows you to transform the URL of such an incoming request to a different URL accord-

ing to a defined set of rules. You could use URL rewriting to transform the previous non-existent URLs

to

product.php?product_id=123

, which

does

exist.

From now on, the chapter tends to be very technical. As a rule of thumb, most exer-

cises you’ll find in this book involve writing code, which at times can get quite

complex. We’ve done our best to explain it, but if you don’t have the technical back-

ground assumed by this book — experience with PHP develop

ment — you may

need assistance in following the examples.

46

Chapter 3: Provocative SE-Friendly URLs

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