Is a URL for copyrighted web content also covered by the copyright?

No if you are sending people out to another site that is the owner of the material it's not infringing on their copyright. It would be infringing if you took the content and posted it on your own site without their permission or claimed it as your own.

Breaching copyright is where you publish someone else data without the consent of the owner etc.

If you provide a link for me, it takes me to a new web site. Its that new web site who is then provide me with the data. Providing they them self have the right to that data, your doing nothing wrong.

As an example.

If I had a link in this message that took you to say a how to cook web site, you following that link and then reading the information is ok.

But if I was to cut and past the cooking instructions on my own web site and present it as my own work, I'm bad. Yet even then it can be done.

You can included information with in your own publication say as a web page providing you give credit where its due.

Also keep in mind that as an owner of data. Say in this example IBM believe you are doing something that is not legal by publishing data they believe they own.

Once established you are legally in the wrong their first action must be to inform you of the problem and demand it stop.

They cant simply dump a invoice on you claiming a million dollars.

Only a court can apply a penalty and direct you pay a compensation to another person.