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URI
IS 373—Web Standards
Todd Will
What’s in a name?
• What is a URI/URL/URN?
• Why are they important?
• What strategies can be used to
manage them?
– Information Architecture
– Content Negotiation
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URI
– A Uniform Resource Identifier (URI) is a
compact string of characters for
identifying an abstract or physical
resource.
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Uniform
• Uniformity:
– Allows different types of resources to be
referenced in the same context
– Allows new types of resources to be
added in the future
– Allows identifiers to be reused in many
different contexts
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Resource
• A resource can be anything that has
identity, e.g.
–
–
–
–
–
Documents
Images
Services, e.g. weather, authentication
People
Books
• Conceptual mapping to an entity or set of
entities, not necessarily the entity which
corresponds to that mapping at any
particular instance in time.
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Identifier
• An identifier is an object that can act
as a reference to something that has
identity. In the case of URI, the object
is a sequence of characters with a
restricted syntax.
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URI vs URN vs URL
• A URI can be further classified as a locator, a name,
or both.
• "Uniform Resource Locator" (URL)
refers to the subset of URI that identify resources via
a representation of their primary access mechanism
(e.g., their network "location"), rather than
identifying the resource by name or by some other
attribute(s) of that resource.
• "Uniform Resource Name" (URN)
refers to the subset of URI that are required to
remain globally unique and persistent even when
the resource ceases to exist or becomes
unavailable.
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URI Format
• <scheme>://<authority><path>?<query>
• Examples:
– http://is.njit.edu/
– ftp://afs2.njit.edu
– mailto:[email protected]?subject=hi%20there
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Cool URI’s Don’t Change
• When you change a URI on your
server, you can never completely tell
who will have links to the old URI.
• When someone follows a link and it
breaks, they generally lose confidence
in the owner of the server. They also
are frustrated - emotionally and
practically from accomplishing their
goal.
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URL Usability
• Which is better?
http://is.njit.edu/index.php?s=courses&c=undergrad&id=144
http://is.njit.edu/courses/undergrad/cis373
http://is.njit.edu/undergrad/cis373
http://is.njit.edu/courses/cis373
http://is.njit.edu/cis373
• Good URL’s can be guessed
• Implication:
– Creating a URL is like having a baby, you
are creating something for which you will
be responsible for a long time
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URL Management
• Information Architecture
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–
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Simple as possible
Predictable/Logical
Descriptive
Uniform
• For larger organization’s sites
maintaining discipline can be difficult
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Content Negotiation
• Can accomplish two things:
– Associate multiple URI’s with the same
resource
• e.g. different links to CIS 373 in previous slide
– Serve different versions of a given
resource depending on the client
• e.g. serve a different version of a page
depending on the browser
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mod_rewrite example
• Sample contents of file .htaccess:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RedirectMatch ^/turoff http://web.njit.edu/~turoff
RedirectMatch ^/hiltz http://web.njit.edu/~hiltz
RedirectMatch ^/bieber http://web.njit.edu/~bieber
RewriteRule ^(.+) - [PT,L]
RewriteRule ^(.*) index.php
</IfModule>
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ISAPI_Rewrite
• Provides functionality similar to
mod_rewrite
• 3rd party software that works with IIS
since IIS doesn’t have a built-in
mechanism for handling URL schemes
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What not to put in your URI
• Authors name – people can quit, be hired, change
authorship
• Subject. Tricky to use, but better
• Status- Don’t use old, new, draft – keep the most
recent document at the same url and archive the
older versions
• Access. If the level of access to the document
changes, then make sure that the url will not break
– Use the same name for the document and the url
• File name extension. Even html file extension can
change if you rewrite your pages in asp or java
• Software mechanisms. Don’t put the software you
are using in the url – the software can change over
time
• Disk name – Big no, no
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Conclusion
• URI’s are an important building block
of the Internet
• It’s important to recognize them for
what they can do for your web based
applications.
• Remember uri’s should be consistent
and not change over time
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For Next Week
• Papers and presentation printouts due
next week
• First set of presentations next week
• Questions or problems with papers
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