Content reference identifier: Difference between revisions

Revision as of 03:27, 9 April 2014

Revision as of 03:30, 9 April 2014

Line 1:

{{Use dmy dates|date=April 2014}}

{{cleanup-reorganize|date=April 2013}}

:''CRID redirects here. CRID may also refer to a Currentcurrent Railrail Indicatorindicator Devicedevice, a safety device which indicates the presence of [[third rail]] power; cf. [http://www.trainweb.org/tubeprune/dictionary.htm], or to a Cherenkov Ringring Imagingimaging Detectordetector [http://www.osti.gov/bridge/purl.cover.jsp?purl=/57182-65UQ1E/57182.pdf].''

== Overview ==

A '''Contentcontent Referencereference Identifieridentifier''' or '''CRID''' is a concept from the standardization work done by the [[TV-Anytime]] forum. It is or closely matches the concept of the [[Uniform Resource Locator]], or URL, as used on the [[World-Wide Web]]:

{{Quotation|A unit of content, in a [[Broadcasting|broadcast stream]], can be referred to by its globally unique CRID in the same way that a [[webpage]] can be referred to by its globally unique URL on the web.}}<!--source? or is it not a quotation?-->

Line 20 ⟶ 21:

== Format ==

A CRID is specified much like URLs. In fact, a CRID is a so-called [[Uniformuniform Resourceresource Identifieridentifier|URI]]. Typically, the content creator, the broadcaster or a third party will use their [[Domain___domain Namename Systemsystem|DNS]]-names in a combination with a product-specific name to create globally unique CRIDs. That is, the syntax of a CRID is:

crid://authority/data

Line 28 ⟶ 29:

crid://bbc.co.uk/olympics/2008/

This would be a group CRID, that is, a CRID representing a group of contents. Then, to refer to a specific event -– such as the women's shot-put final -– they could have used the following inside their metadata.

crid://bbc.co.uk/olympics/2008/final/shotput/women

Currently,{{When|date=January 2013}} four types of CRIDs are playing a major role in some [[Unidirectional networks|unidirectional]] [[television network]]snetworks: programme CRID, series CRID, group CRID, and recommendation CRID. One of the most important applications of CRIDs is the so-called series link recording function (SL) of modern digital video recorders ([[Digital video recorder|DVR]], [[Personal video recorder|PVR]]).

In turn, a locator is a string of characters that contains all the necessary information for a receiver to find and acquire a given content, whether it is received through a transport stream, located in local storage, downloaded as a file from an Internet server, or through a streaming service. For example, a DVB locator will include all the necessary parameters to identify a specific content within a transport stream: network, transport stream, service, table and/or event identifiers.

Line 40 ⟶ 41:

The first part of the locator’s format (the transport mechanism) must be a string of characters that is unique for each mechanism (transport stream, local file, HTTP Internet access…). The second part must be unambiguous only within the scope of a given transport mechanism and will be standardized by the organism in charge of the regulation of the mechanism itself.

For instance, a DVB locator to identify a content within the transport stream of networks that follow this standard would be:

dvb://112.4a2.5ec;2d22~20121212T220000Z—PT01H30M, which would indicate a content (identified by the string “2d22”) that airs on a channel available on a DVB network identified by the address “112.4a2.5ec” (network “112”, transport stream “4a2” and service “5ec”), on 12/12/ December 2012 at 10 p.m. and with a duration of 90 minutes.

dvb://112.4a2.5ec;2d22~20121212T220000Z—PT01H30M

which would indicate a content (identified by the string “2d22”) that airs on a channel available on a DVB network identified by the address “112.4a2.5ec” (network “112”, transport stream “4a2” and service “5ec”), on 12/12/2012 at 10 p.m. and with a duration of 90 minutes.

== The ___location resolution process ==

Line 48 ⟶ 47:

The ___location resolution process is the procedure by which, starting from the CRID of a given content, one or several locators of that content are obtained. Resolving a CRID can be a direct process, which leads immediately to one or many locators, or it may also happen that in the first place one or many intermediate CRIDs are returned, which must undergo the same procedure to finally obtain one or several locators.

This procedure involves some information elements, among which we find two structures named Resolvingresolving Authorityauthority Recordrecord (RAR) and ContentReferencingTable, respectively. Consulting them repeatedly will take the receiver from a CRID to one or many locators that will allow it to acquire the content.

'''The RAR table'''

The RAR table is one or many data structures that provide the receiver, for each authority that submits CRIDs, information on the corresponding resolution service provider. Among other things, it also informs about which mechanism is used to provide information to resolve the CRIDs from each authority. That is, one or many RAR records must exist for each authority that indicate the receiver where it has to go to resolve the CRIDs of that particular authority.

For example, in the record of the figure (expressed by means of a XML structure, according to the XML Schema defined in the TV-Anytime) there is an authority called “tve.es”, whose resolution service provider is the entity “rtve.es”, available on the URL <nowiki>"http://tva.rtve.es/locres/tve"</nowiki>, which means there is resolution information in that URL.

Line 62 ⟶ 61:

'''The ContentReferencingTable table'''

The second structure involved in the ___location resolution process is a proper resolution table which, given a content’scontent's CRID, returns one or several locators that enable the receiver to access an instance of that content, or one or many CRIDs that allow it to move forward in the resolution process.

The figure shows an example of this second structure, an XML document according to the specifications of the XML Schema defined in TV-Anytime. In it, several sections are included (<Result> elements) that structure the information that describes each resolution case.

Line 91 ⟶ 90:

In May 2005, an Informational RFC, [http://tools.ietf.org/html/rfc4078 No 4078], was published as the start of this work.

The long-term goal is that CRIDs should be available for use by [[cell phones]], [[Personal digital assistant|PDA]]s, [[Digital television|digital TV]] [[Set-top box|receivers]] and other [[Consumer electronics|consumer devices]] for fetching content, either from a broadcast stream or over [[Internetinternet Protocolprotocol|IP]]-based [[computer network|networks]].

== References ==

* [ftp://ftp.rfc-editor.org/in-notes/pdfrfc/rfc4078.txt.pdf RFC 4078 (PDF)] Accessed 27 October 2011

* [ftp://ftp.rfc-editor.org/in-notes/rfc4078.txt RFC 4078 (TXT)] Accessed 27 October 2011

* [http://www.etsi.org/deliver/etsi_ts/102800_102899/10282202/01.04.01_60/ts_10282202v010401p.pdf ETSI TS 102 822-2 V1.4.1 (2007-112007–11), Page 19, Section 5: "TV-Anytime content referencing scenarios"] Accessed 3 December 2012

* [http://www.etsi.org/deliver/etsi_ts/102800_102899/10282204/01.07.01_60/ts_10282204v010701p.pdf ETSI TS 102 822-4 V1.7.1 (2012-122012–12), Page 13, Section 8: "CRID"] Accessed 9 January 2013

* [http://www.etsi.org/deliver/etsi_ts/102300_102399/102323/01.05.01_60/ts_102323v010501p.pdf ETSI TS 102 323 V1.5.1 (2012-01), Page 27, Section 6: "CRIDs and other URIs in DVB networks"] Accessed 1 March 2012

<!-- THIS SECTION IS BECOMING A WP:LINKFARM AND THE REFERENCES ARE UNCLEAR