Appendix A. URI Schemes

Appendix A. URI Schemes

Many URI schemes have been defined, but few are in common use. Generally speaking, those URI schemes with associated RFCs are in more common use, though there are a few schemes that have been developed by leading software corporations (notably Netscape and Microsoft), but not formalized , that also are in wide use.

The W3C maintains a list of URI schemes, which you can view at:

http://www.w3.org/Addressing/schemes.html

The IANA also maintains a list of URL schemes, at:

http://www.iana.org/assignments/uri-schemes

Table A-1 informally describes some of the schemes that have been proposed and those that are in active use. Note that many of the approximately 90 schemes in the table are not widely used, and many are extinct.

Table A-1. URI schemes from the W3C registry
Scheme	Description	RFCs
about	Netscape scheme to explore aspects of the browser. For example: about by itself is the same as choosing "About Communicator" from the Navigator Help menu, about:cache displays disk-cache statistics, and about:plugins displays information about configured plug-ins. Other browsers, such as Microsoft Internet Explorer, also use this scheme.
acap	Application Configuration Access Protocol.	2244
afp	For file-sharing services using the Apple Filing Protocol (AFP) protocol, defined as part of the expired IETF draft-ietf-svrloc-afp-service-01.txt .
afs	Reserved for future use by the Andrew File System.
callto	Initiates a Microsoft NetMeeting conference session, such as: callto: ws3.joes-hardware.com/[e-mail]
chttp	The CHTTP caching protocol defined by Real Networks. RealPlayer does not cache all items streamed by HTTP. Instead, you designate files to cache by using chttp:// instead of http:// in the file's URL. When RealPlayer reads a CHTTP URL in a SMIL file, it first checks its disk cache for the file. If the file isn't present, it requests the file through HTTP, storing the file in its cache.
cid	The use of [MIME] within email to convey web pages and their associated images requires a URL scheme to permit the HTML to refer to the images or other data included in the message. The Content-ID URL, "cid:", serves that purpose.	23922111
clsid	Allows Microsoft OLE/COM (Component Object Model) classes to be referenced. Used to insert active objects into web pages.
data	Allows inclusion of small, constant data items as "immediate" data. This URL encodes the text/plain string "A brief note": data:A%20brief%20note	2397
date	Proposal for scheme to support dates, as in date:1999-03-04T20:42:08 .
dav	To ensure correct interoperation based on this specification, the IANA must reserve the URI namespaces starting with "DAV:" and with "opaquelocktoken:" for use by this specification, its revisions, and related WebDAV specifications.	2518
dns	Used by REBOL software. See http://www.rebol.com/users/valurl.html .
eid	The external ID (eid) scheme provides a mechanism by which the local application can reference data that has been obtained by other, non-URL scheme means. The scheme is intended to provide a general escape mechanism to allow access to information for applications that are too specialized to justify their own schemes. There is some controversy about this URI. See http://www.ics.uci.edu/pub/ietf/uri/draft-finseth-url-00.txt .
fax	The "fax" scheme describes a connection to a terminal that can handle telefaxes ( facsimile machines).	2806
file	Designates files accessible on a particular host computer. A hostname can be included, but the scheme is unusual in that it does not specify an Internet protocol or access method for such files; as such, its utility in network protocols between hosts is limited.	1738
finger	The finger URL has the form: finger://host[:port][/<request>] The <request> must conform with the RFC 1288 request format. See http://www.ics.uci.edu/pub/ietf/uri/draft-ietf-uri-url-finger-03.txt .
freenet	URIs for information in the Freenet distributed information system. See http://freenet. sourceforge .net .
ftp	File Transfer Protocol scheme.	1738
gopher	The archaic gopher protocol.	1738
gsm-sms	URIs for the GSM mobile phone short message service.
h323, h324	Multimedia conferencing URI schemes. See http://www.ics.uci.edu/pub/ietf/uri/draft-cordell-sg16-conv-url-00.txt .
hdl	The Handle System is a comprehensive system for assigning, managing, and resolving persistent identifiers, known as "handles," for digital objects and other resources on the Internet. Handles can be used as URNs. See http://www.handle.net .
hnews	HNEWS is an HTTP-tunneling variant of the NNTP news protocol. The syntax of hnews URLs is designed to be compatible with the current common usage of the news URL scheme. See http://www.ics.uci.edu/pub/ietf/uri/draft-stockwell-hnews-url-00.txt .
http	The HTTP protocol. Read this book for more information.	2616
https	HTTP over SSL. See http://sitesearch.netscape.com/eng/ssl3/draft302.txt .
iioploc	CORBA extensions. The Interoperable Name Service defines one URL-format object reference, iioploc, that can be typed into a program to reach defined services at remote locations, including the Naming Service. For example, this iioploc identifier: iioploc://www.omg.org/NameService would resolve to the CORBA Naming Service running on the machine whose IP address corresponded to the domain name www.omg.org . See http://www.omg.org .
ilu	The Inter-Language Unification (ILU) system is a multilingual object interface system. The object interfaces provided by ILU hide implementation distinctions between different languages, different address spaces, and different operating system types. ILU can be used to build multilingual object-oriented libraries ("class libraries") with well-specified, language-independent interfaces. It also can be used to implement distributed systems. See ftp://parcftp.parc.xerox.com/pub/ilu/ilu.html .
imap	The IMAP URL scheme is used to designate IMAP servers, mailboxes, messages, MIME bodies [MIME], and search programs on Internet hosts accessible using the IMAP protocol.	2192
IOR	CORBA interoperable object reference. See http://www.omg.org .
irc	The irc URL scheme is used to refer to either Internet Relay Chat (IRC) servers or individual entities (channels or people) on IRC servers. See http://www.w3.org/Addressing/draft-mirashi-url-irc-01.txt .
isbn	Proposed scheme for ISBN book references. See http://lists.w3.org/Archives/Public/www-talk/1991NovDec/0008.html .
java	Identifies Java classes.
javascript	The Netscape browser processes javascript URLs, evaluates the expression after the colon (:), if there is one, and loads a page containing the string value of the expression, unless it is undefined.
jdbc	Used in the Java SQL API.
ldap	Allows Internet clients direct access to the LDAP protocol.	2255
lid	The Local Identifier (lid:) scheme. See draft-blackketter-lid-00 .
lifn	A Location-Independent File Name (LIFN) for the Bulk File Distribution distributed storage system developed at UTK.
livescript	Old name for JavaScript.
lrq	See h323.
mailto	The mailto URL scheme is used to designate the Internet mailing address of an individual or service.	2368
mailserver	Old proposal from 1994-1995 to let an entire message be encoded in a URL, so that (for example) the URL can automatically send email to a mail server for subscribing to a mailing list.
md5	MD5 is a cryptographic checksum.
mid	The mid scheme uses (a part of) the message-id of an email message to refer to a specific message.	23922111
mocha	See javascript.
modem	The modem scheme describes a connection to a terminal that can handle incoming data calls.	2806
mms, mmst, mmsu	Scheme for Microsoft Media Server (MMS) to stream Active Streaming Format (ASF) files. To force UDP transport, use the mmsu scheme. To force TCP transport, use mmst.
news	The news URL scheme is used to refer to either news groups or individual articles of USENET news. A news URL takes one of two forms: news:<newsgroup-name> or news:<message-id> .	17381036
nfs	Used to refer to files and directories on NFS servers.	2224
nntp	An alternative method of referencing news articles, useful for specifying news articles from NNTP servers. An nntp URL looks like: nntp://<host>:<port>/<newsgroup-name>/<article-num> Note that while nntp URLs specify a unique location for the article resource, most NNTP servers currently on the Internet are configured to allow access only from local clients, and thus nntp URLs do not designate globally accessible resources. Hence, the news form of URL is preferred as a way of identifying news articles.	1738977
opaquelocktoken	A WebDAV lock token, represented as a URI, that identifies a particular lock. A lock token is returned by every successful LOCK operation in the lockdiscovery property in the response body and also can be found through lock discovery on a resource. See RFC 2518.
path	The path scheme defines a uniformly hierarchical namespace where a path URN is a sequence of components and an optional opaque string. See http://www.hypernews.org/~liberte/www/path.html .
phone	Used in "URLs for Telephony"; replaced with tel: in RFC 2806.
pop	The POP URL designates a POP email server, and optionally a port number, authentication mechanism, authentication ID, and/or authorization ID.	2384
pnm	Real Networks's streaming protocol.
pop3	The POP3 URL scheme allows a URL to specify a POP3 server, allowing other protocols to use a general "URL to be used for mail access" in place of an explicit reference to POP3. Defined in expired draft-earhart-url-pop3-00.txt .
printer	Abstract URLs for use with the Service Location standard. See draft-ietf-srvloc-printer-scheme-02.txt .
prospero	Names resources to be accessed via the Prospero Directory Service.	1738
res	Microsoft scheme that specifies a resource to be obtained from a module. Consists of a string or numerical resource type, and a string or numerical ID.
rtsp	Real-time streaming protocol that is the basis for Real Networks's modern streaming control protocols.	2326
rvp	URLs for the RVP rendezvous protocol, used to notify the arrival of users on a computer network. See draft-calsyn-rvp-01 .
rwhois	RWhois is an Internet directory access protocol, defined in RFC 1714 and RFC 2167. The RWhois URL gives clients direct access to rwhois. See http://www.rwhois.net/rwhois/docs/ .
rx	An architecture to allow remote graphical applications to display data inside web pages. See http://www.w3.org/People/danield/papers/mobgui/ .
sdp	Session Description Protocol (SDP) URLs. See RFC 2327.
service	The service scheme is used to provide access information for arbitrary network services. These URLs provide an extensible framework for client-based network software to obtain configuration information required to make use of network services.	2609
sip	The sip* family of schemes are used to establish multimedia conferences using the Session Initiation Protocol (SIP).	2543
shttp	S-HTTP is a superset of HTTP designed to secure HTTP connections and provide a wide variety of mechanisms to provide for confidentiality, authentication, and integrity. It has not been widely deployed, and it has mostly been supplanted with HTTPS SSL-encrypted HTTP. See http://www.homeport.org/~adam/shttp.html .
snews	SSL-encrypted news.
STANF	Old proposal for stable network filenames. Related to URNs. See http://web3.w3.org/Addressing/#STANF .
t120	See h323.
tel	URL to place a call using the telephone network.	2806
telephone	Used in previous drafts of tel.
telnet	Designates interactive services that may be accessed by the Telnet protocol. A telnet URL takes the form: telnet://< user >:<password>@<host>:<port>/	1738
tip	Supports TIP atomic Internet transactions.	23712372
tn3270	Reserved, as per ftp://ftp.isi.edu/in-notes/iana/assignments/url-schemes .
tv	The TV URL names a particular television broadcast channel.	2838
uuid	Universally unique identifiers (UUIDs) contain no information about location. They also are known as globally unique identifiers (GUIDs). They are persistent over time, like URNs, and consist of a 128-bit unique ID. UUID URIs are useful in situations where a unique identifier is required that cannot or should not be tied to a particular physical root namespace (such as a DNS name). See draft-kindel-uuid-uri-00.txt .
urn	Persistent, location-independent, URNs.	2141
vemmi	Allows versatile multimedia interface (VEMMI) client software and VEMMI terminals to connect to VEMMI-compliant services. VEMMI is an international standard for online multimedia services.	2122
videotex	Allows videotex client software or terminals to connect to videotex services compliant with the ITU-T and ETSI videotex standards. See http://www.ics.uci.edu/pub/ietf/uri/draft-mavrakis-videotex-url-spec-01.txt .
view-source	Netscape Navigator source viewers . These view-source URLs display HTML that was generated with JavaScript.
wais	The wide area information servicean early form of search engine.	1738
whois++	URLs for the WHOIS++ simple Internet directory protocol. See http://martinh.net/wip/whois-url.txt .	1835
whodp	The Widely Hosted Object Data Protocol (WhoDP) exists to communicate the current location and state of large numbers of dynamic, relocatable objects. A WhoDP program "subscribes" to locate and receive information about an object and "publishes" to control the location and visible state of an object. See draft-mohr-whodp-00.txt .
z39.50r, z39.50s	Z39.50 session and retrieval URLs. Z39.50 is an information retrieval protocol that does not fit neatly into a retrieval model designed primarily around the stateless fetch of data. Instead, it models a general user inquiry as a session-oriented, multi-step task, any step of which may be suspended temporarily while the server requests additional parameters from the client before continuing.	2056