View source for Relationships: An essential component of art and culture

''From the [[TC 372 Workshop Compendium]]''

==Giving spice to metadata==

Why do we add something to a collection of an archive, a museum, or a library? We do not add something because it weighs 3.5 kilograms, is of blue color, or is made of cardboard. We rather add it because it '''relates to something we know''', and possibly, to other things in ways we still have to '''discover'''.

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http://commons.wikimedia.org/wiki/File:2006-10-15_Tasse%2BUntertasse-Pflaume01.jpg
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'''Trash or treasure?''' It all depends on relationships.

Who drank from this cup? Was it someone important? Who was the previous owner? Is it a rare specimen or does it exist in thousands of exemplars? Who created the design and who manufactured it? Is it a specimen of an important artistic style?

And perhaps most importantly: '''was it used in''' the set decoration for '''a film?'''
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| valign="top" width="405px" |[[File:Cidoc-crm-prop.png|400px]]<br /> 
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From: Definition of the CIDOC Conceptual Reference Model, Version 4.2.5a. CIDOC CRM Special Interest Group, September 2008
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A small excerpt from the list of '''relationships''' (referred to as ''properties'' in this context) from the CIDOC Conceptual Reference Model (CRM). Originally motivated by the requirements of museums, this model had (and continues to have) a profound impact on metadata activities throughout the cultural heritage sector.

The CIDOC CRM is an elaborate example of what is also known as a ''domain ontology''.
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'''hasAsSubject''' is one of the relationships defined in EN 15907.

In its '''forward''' form, it says that something '''has''' something else '''as subject''' (i.e. is about the subject). 

In its '''inverse''' form, it says that someting '''is the subject of''' something else.

Relationships with an inverse form are said to be asymmetric.
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| valign="top" width="405px" |[[File:Sfi-music-piece.png|400px]]<br /> 
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From: http://www.sfi.se/en-gb/Swedish-film-database/Item/?type=MUSIC&itemid=1688
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Here is a record for a '''musical work''' as part of a filmographic database.

EN 15907 defines a '''HasOtherRelation''' element that can be used to relate cinematographic works to '''non-film works such as music'''. 
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'''Musical works''' need to be performed in order to be useful in a film.

If a suitably detailed music database is available, then the cinematographic work can be linked to a '''performance'''.

If not, then the target for the ''uses music'' relationship can be described in plain text. 
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''Jazzgossen'' has another interesting relationship: it '''uses''' clips from an '''earlier film work''' starring Lars Hanson.

Thus we have an '''indirect relationship''' for at least one actor. This is sometimes referred to as '''transclusion'''. 
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'''Using''' a clip from a '''pre-existing work''' does not mean that all properties of the included film become properties of the new work.

In this case, '''only some actors''' from the earlier film can be seen in Jazzgossen. The SFI database accounts for this by defining a compilation entity which is used to selectively associate persons and other entities with the compiled work.

The compilation entity can be modelled straightforwardly as a specialisation of an EN 15907 '''production event'''.
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==Relationships and the Web==

Cultural heritage studies consist to a large part in elucidating relationships. To date, the World Wide Web has only been marginally useful for '''transforming relationships''' from printed prose '''into a navigable data space'''. To a machine, a hyperlink is just a jump target that leads from one document to another in an unspecified way. Can we do better? 

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From: Tim Berners-Lee and Daniel Connolly: Hypertext Markup Language. Internet Draft, 1993. http://www.w3.org/MarkUp/draft-ietf-iiir-html-01.txt
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Initially, in 1993, the Hypertext Markup Language (HTML) was designed with elements that would allow computers to distiguish between e.g. author, address, content, etc., and even between '''different kinds of links'''. As the Web began to grow, this idea did not catch on and HTML was used primarily as a text formatting language.

It took another decade before the idea of '''semantic''' tags and links started to spread.
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From: http://dbpedia.org/page/Cimarron_%281960_film%29 accessed 12-Oct-2010
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In 2009, the World Wide Web Consortium (W3C) started introducing a new facility for semantic linking in conjunction with version 5 of the HTML specification.

Termed RDFa, this HTML extension allows for expressing relationships according to the '''RDF data model'''. RDF is designated as the backbone for most of what is becoming known as the semantic web. '''Marked up''' using RDFa, factual '''statments''' can be '''extracted''' from text such that they can be transformed, queried, or used in inference chains.
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"Modell zum Durchstoßverfahren der Perspektive nach Brunelleschi, gebaut nach den Darstellungen von Albrecht Duerer". http://www.aida.uni-hannover.de/aida/max/70~Forschung/Darstellungsgrundlagen/
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Apart from telling what different things have to do with each other, relationship statements are also used to explain the degree and kind of '''similarity''' between things.

Similarity relationships are known as '''mappings''', a term borrowed from mathematics. The activity of establishing such relationships is sometimes referred to as '''matching'''.
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Finally, these are the '''many-to-many relationships''' defined in EN 15907. 

Entities shown in red are the '''domains''' to which the relationship is applicable. Entities shown in blue are those defined as the '''range''' of the relationship.

In Web-based user interfaces, relationships such as these will usually be presented as links leading to the target (i.e. the ''range'' element) of the relationship. Most many-to-many relationships also have '''inverse forms''' that will be used to navigate the data space in the reverse direction.
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