Understanding Absolute and Relative URL Addressing

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Microsoft FrontPage uses absolute URL addressing. However, FrontPage does provide a way to change the addressing of URLs between absolute and relative addressing through the MakeRel and MakeAbs methods.

What is an absolute URL?

A URL defines the location of an object. When an URL is absolute, it defines unambiguously where the object is located. For example, http://www.microsoft.com/FrontPage/default.htm is the exact location of the welcome page for Microsoft FrontPage. The object, default.htm, is stored in the FrontPage folder or subweb on the web server, www.microsoft.com.

A disk-based web that contains your webs on your hard drive might have a base absolute URL such as file:///C:/My Documents/My Webs or C:/WINNT/Profiles/your logon alias/Personal/My Webs/index.htm.

As Web sites are updated and the structure of a web evolves, documents can often be moved from one location to another in a web. If you're using a relative address, you may break some links. For example, if you have a document that has a hyperlink to an object, you can use an absolute URL to insure that the hyperlink always refers to that object. For example, a document such as file:///C:/My Documents/My Webs/mydocument.htm, may contain an absolute URL that refers to the welcome page, http://www.microsoft.com/FrontPage/default.htm. If the document, default.htm, is moved to another location, the absolute URL for the document will always refer to the object on the web server at www.microsoft.com in the subweb, FrontPage. If the URL for the hyperlink to default.htm is a relative address, the link could be broken if mydocument.htm is moved to a different subweb or main web.

What is a relative URL?

Instead of specifying every piece of a URL that fully defines how to find an object, you can abbreviate a URL to make it relative to a current location. Relative URLs are typically used when creating a web site in which the pages in it refer to other pages on the site. A page such as file:///C:/My Documents/My Webs/mydocument.htm can have a relative URL to newdocument,htm or to ../My Webs2/default.htm. In these two cases, the referred addresses for these files are file:///C:/My Documents/My Webs/newdocument.htm and file:///C:/My Documents/My Webs2/default.htm. Notice that the full web server or explicit directory isnt specified, the location is based on where the document is located.

Relative URLs are very useful, particularly when constructing a site in one place, and then publishing it to another place. For example, you might not want to specify a server name while authoring a web page, because the server name will change when the web is published.

How can an absolute URL be made relative?

URLs can be made relative either to a server or to a page. In order to make a URL relative to a folder or to a web, you need to make the URL relative either to a server or to a page, because FrontPage will treat the URL as if it were being made relative to a page in that folder or web. Each relative URL, combined with its base URL fully specifies where the object is located.

When you have an absolute address such as http://www.microsoft.com/myweb, with an image file called MyPicture.gif residing in the images folder on the web, you can create a relative URL for that address by deciding whether the relative address will refer to a server or a page. For a server relative URL, youd use myweb/images/MyPicture.gifwith the server name as the base for the relative URL, this relative address fully defines the location of the object. For a page relative URL, youd use images/MyPicture,gifwith theserver name and the web name as the base for the relative URL, this relative address fully defines the location of the object. For a folder relative URL, youd use MyPicture.gifwith the server name, web name, and folder name as the base for the relative URL, this relative address fully defines the location of the object.

A folder relative URL can also be specified from a different folderfor example, ../images/MyPicture.gif could be used if the referring document was in another top level folder on the same web and server. The .. is the notation used to indicate up one folder level from the current URL address.

Programmatic Access to Relative URLs

Once you've decided whether to use server, web, or folder relative URLs, you can determine which objects to use. For server or web relative URLs, you would be working with methods related to the Web object. For folder relative URLs, you would be working with methods related to the WebFolder object.

Converting relative and absolute URLs

Recommended use for FrontPage is absolute addressing. However, once you have specified relative URL within FrontPage, you can use the MakeAbs method to convert it into an absolute URL. Similarly, if you have an absolute URL, and you want to insert a reference into a document as a relative URL, you can use MakeRel to convert the address to a relative address. You can also use the MakeAbs and MakeRel methods to convert a hyperlink for a Web, WebFolder, WebFile, NavigationNode, or IHTMLDocument2 object.