Content reference identifier: Difference between revisions

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:''{{hatnote|1=CRID redirects here. CRID may also refer to a Currentcurrent Railrail Indicatorindicator Devicedevice, a safety device which indicatesindicating the presence of [[third rail]] power; cf. [http://www.trainweb.org/tubeprune/dictionary.htm], or to a [[Ring-imaging Cherenkov detector|Cherenkov Ring -Imaging Detector [http://www.osti.gov/bridge/purl.cover.jsp?purl=/57182-65UQ1E/57182.pdf].'']}}

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]]:

== Overview ==

A '''Content Reference Identifier''' 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?-->

The concept of CRID permits to referencereferencing contents unambiguously, regardless of their ___location, i.e., without knowing specific broadcast information (time, date and channel) or how to obtain them through a network, for instance, by means of a streaming service or by downloading a file from an Internet server.

The receiver must be capable of resolving these unambiguous references, i.e., translateof translating them into specific data that will allow it to obtain the ___location of that content in order to acquire it. This makes it possible for recording processes to take place without knowing that information, and even without knowing beforehand the duration of the content to be recorded: a complete series by a simple click, a program that has not been scheduled yet, a set of programs grouped by a specific criterion…

This framework allows for the separation between the reference to a given content (the CRID) and the necessary information to acquire it, which is called a “locator”. Each CRID may lead to one or more locators which will represent different copies of the same content. They may be identical copies broadcast in different channels or dates, or cost different prices. They may also be distinct copies with different technical parameters such as format or quality.

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It may also be the case that the resolution process of a CRID provides another CRID as a result (for example, its reference in a different network, where it has an alternative identifier assigned by a different operator) or a set of CRIDs (for instance, if the original CRID represents a TV series, in which case the resolution process would result in the list of CRIDs representing each episode).

From the above it iscan obviousbe concluded that, provided that a given content can belong to many groups (each possibly defined by distinctive qualities), it is possible that many CRIDs carry the same content. That is, several CRIDs may be resolved into the same locator.

A CRID is not exactly a universal, unique and exclusive identifier for a given content. It is closely related to the authority that creates it, to the resolution service provider, and to the content provider in such a way that the same content may have different CRIDs depending on the field in which they are used (for example, a different one for each television operator that has the rights to broadcast the content).

== 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

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As an example, let's assume that [[BBC]] wanted to make a CRID for (all the programs of) the Olympics in China. It may have looked something like this

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.

The locators’locators' format, as established in TV-Anytime, is quite generic and simple, and corresponds to:

<[transport-mechanism>]:<[specific-data>]

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.

== The ___location resolution process ==

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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.

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'''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.

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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 [[Internet Protocol|IP]]-based [[computer network|networks]]s.

== OverviewSee also ==

* [[BBC Programme Identifier]]

== References ==

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

* [ftphttp://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

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