... can somebody please explain to me what the URI is?
A URI stands for Unique Resource Identifier. It is a standard for accessing resources (be they content, data, or execution) across a network of devices (most often a wide area network). URIs are used for a ton of things, including Android packages, ActiveDirectory, the entire WWW, FTP, Gopher, even accessing hard drive data uses an outdated URI convention. A URL is a type of URI. URIs are built in the following way:
scheme://host/path/resource#position?params
Example:
In the URL (htt.p://forums.modx.com/thread/78683/uri-not-updated-after-save#dis-post-433707), http is the scheme, forums.modx.com is the host, thread/78683 is the path, uri-not-updated-after-save is the resource, dis-post-433707 is the position and there are no parameters.
So, for the purposes of MODx, the URI is also equivalent to the URL.
And why there should be a checkbox for freezing it?
This is because most broken links on pages are due to alias changes and structure change. If the URL changes after it is live this can have dramatic effects upon your site, its indexing, and its search results placement. Further, if there are link-backs, all of those break.
Freezing the URI can make sure that no matter your changes, the page will always be at the same address (as long as it isn't deleted). The will make sure that search results aren't diluted, manual links aren't broken, and engine placement remains contingent upon the evaluated comparative criteria of competitive sites. (Hint: This is why wikis often have so many redirects)
Further Notes:
Freeze URI should never or rarely be used on a development site before it goes live. In general, it should rarely be used unless you cannot afford to: either a) deal with the "lag time" between index additions, changes and removals; or b) rely on link-backs to fix themselves. There are many "better practices" in lots of others' opinions. You could create a permanent redirect, which would fix the link-backs and indexing all at once, for instance.
[ed. note: fuzzicallogic last edited this post 14 years, 1 month ago.]