PB138 Metadata Describing XML Resources. (C) 2018 Masaryk University --- Tomáš Pitner, Luděk Bártek, Adam Rambousek

Transcription

1 PB138 Metadata Describing XML Resources (C) 2018 Masaryk University --- Tomáš Pitner, Luděk Bártek, Adam Rambousek

2 Metadata Frameworks Describing the XML and Data Resources What is Metadata "Data about data" eg. author of a document/picture/web Date of creation Mode of use (e.g. copyright) Mandate for creation Metadata Purpose Search in data is sometimes difficult without metadata E.g. in multimedia data Sometimes not possible at all (eg. usage mode, mandate ) Facilitates use (eg. by specifying format) Metadata Activities, Models and Representations Linked Data - method of publishing structured data so that it can be interlinked (also Linked Open Data) RDF - general purpose metadata model (Google) Structured Data - primarily web search incl. custom Dublin Core - general purpose metadata set RDF Framework RDF Model and RDF Schema are W3C Recommendation. link: [Specification and further W3C Working Group information] RDF Model RDF is general mechanism for metadata specification can be used with any (not only digital) resources. RDF model is based on triplets: 1

3 resource - for example property - eg. textual description value - PB138 at FI MU Homepage for example. Triplets can be represented: graphically, like a triplets (r, p, v) by an XML syntax RDF Model - Further Reading Good introduction on xml.com: What is RDF? Zvon RDF Tutorial RDF Tutorial - W3Schools RDF Tutorial RDF Tutorial RDF Schema Specifies the set of properties and their definition domain and the range of their values. To model the RDF Schema is used the RDF. RDF representation of used metadata schemes - Z39.50, Dublin Core etc. RDF is general framework for metadata modelling. There is a need of definition of allowed properties, their domains and (allowed) for particular use. This is the way to create RDF metadata schema representation. Representation may be in a form of RDF Schema. Dublin Core The Dublin Core Metadata Element Set is a vocabulary of 15 properties for use in resource description, Dublin (OH, USA) - first workshops core - its elements are broad and generic, usable for describing a wide range of resources. Based on initiative of librarians to create framework for bibliographic information description. Created by 15 basic elements with partially defined semantics. 2

4 Elements can be extended - by decomposition to (usually disjoint) subsets. An extended element always must be a subset of an originally designed element. Dublin Core Standardisation ISO Standard 15836:2009 of February 2009 [ISO15836] ANSI/NISO Standard Z of February 2013 [NISOZ3985] IETF RFC 5013 of August 2007 [RFC5013] Simple Dublin Core "Simple" or "unqualified" Dublin Core ("Simple DC" in what follows) represents the basic set of 15 element designed and supported by: Dublin Core Metadata Initiative (DCMI, Present version - Dublin Core 1.1. Accepted by IETF consortium as RFC (Request For Comment) 2431 as well as ISO Standard since Dublin Core - elements Title / Název - Jméno dané zdroji / A name given to the resource. Creator / Tvůrce - An entity primarily responsible for making the resource. / Entita primárně odpovědná za vytvoření obsahu zdroje Subject / Předmět a klíčová slova - The topic of the resource. / Téma obsahu zdroje Description / Popis - An account of the resource. / Vysvětlení obsahu zdroje Publisher / Vydavatel - An entity responsible for making the resource available. / Entita odpovědná za zpřístupnění zdroje Contributor / Přispěvatel - An entity responsible for making contributions to the resource / Entita, která přispěla k vytvoření obsahu zdroje Date / Datum - A point or period of time associated with an event in the lifecycle of the resource. / Datum spojené s určitou události během existence zdroje Type / Typ zdroje - The nature or genre of the resource. / Povaha nebo druh obsahu zdroje Format / Format - The file format, physical medium, or dimensions of the resource. / Fyzická nebo digitalní reprezentace zdroje Dublin Core - elements (cont.) Identifier / Identifikátor zdroje - An unambiguous reference to the resource within a given context. / Jednoznačný odkaz na zdroj v rámci daného kontextu 3

5 Source / Zdroj - A related resource from which the described resource is derived. / Odkaz na zdroj, z něhož je popisovaný zdroj odvozen Language / Jazyk - A language of the resource. / Jazyk intelektualního obsahu zdroje Relation / Vztah - A related resource. / Odkaz na příbuzný zdroj Coverage / Pokrytí - The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant./rozsah nebo záběr obsahu zdroje Rights / Práva - Information about rights held in and over the resource. / Informace o právech vztahujících se k popisovanému zdroji more details at DC - Metadata description example Nazev: Zelena kniha o elektronickem obchodu Tvurce: Urad pro verejne informacni systemy, Urad vlady Predmet: Elektronicky obchod, elektronicky podpis, bezpecnost, sprava Popis: Vladni navrh podpory elektronickeho obchodu v Ceske republice Datum vytvoreni: Datum zverejneni: Identifikator: ISBN:????? Qualified Dublin Core Contains the same set of elements as the Simple DC and recommends more in depth specification and limitation on every element. Typically based on formal or de-facto international standard. E.g. The language must be specified according the ISO 639 standard for example. DC Encodings Plaintext HTML metatags XML RDF RDF Tools Jena Java RDF API and toolkit The ICS-FORTH RDFSuite 4

6 DC Creator on University of Bath for more see RDFa RDFa is an extension to HTML5 that helps you markup things like People, Places, Events, Recipes and Reviews. Search Engines and Web Services use this markup to generate better search listings. Standard Specification at (2015) RDFa Structure RDFa Lite consists of five simple attributes: vocab typeof property resource prefix RDFa Sample RDFa, like Microformats [microformats] and Microdata [microdata], enables us to talk about things on the Web such that a machine can understand what we are saying. Typically when we talk about a thing, we use a particular vocabulary to talk about it. If it is about People, then the vocabulary specifies terms like name and telephone number. Simple example that specifies a vocabulary that we intend to use to markup things in the paragraph: vocab now specified <p vocab=" My name is Manu Sporny and you can give me a ring via </p> RDFa Sample (cont) typeof now specified 5

7 <p vocab=" typeof="person"> My name is Manu Sporny and you can give me a ring via </p> RDFa Sample (cont) property now specified <p vocab=" typeof="person"> My name is <span property="name">manu Sporny</span> and you can give me a ring via <span property="telephone"> </span> or visit <a property="url" href=" homepage</a>. </p> RDFa Sample (cont) resource now specified - for further reference, like "id" attribute in HTML <p vocab=" resource="#manu" typeof="person"> My name is <span property="name">manu Sporny</span> and you can give me a ring via <span property="telephone"> </span>. <img property="image" src=" /> </p> RDFa Sample (cont) prefix now specified - for further extensibility/customization - own vocabulary 6

8 <p vocab=" prefix="ov: resource= "#manu" typeof="person"> My name is <span property="name">manu Sporny</span> and you can give me a ring via <span property="telephone"> </span>. <img property="image" src=" /> My favorite animal is the <span property="ov:preferredanimal">liger</span>. </p> RDFa prefixes This list of predefined prefixes have been defined for RDFa as an initial context RDFa users can use these prefixes without having the obligation of defining the prefixes in the HTML code. The same list of prefixes have also been defined for JSON-LD as a JSON-LD Context International Resource Identifier (IRI) IRI is an extension of URI (Uniform Resource Identifier) defined in [RFC3986] as a sequence of characters chosen from a limited subset of the repertoire of US-ASCII characters. Internationalized Resource Identifier (IRI) is extending the syntax of URIs to a much wider repertoire of characters. It also defines "internationalized" versions corresponding to other constructs from [RFC3986], such as URI references. Linked Data Tim Berners-Lee (TED 2009 conference), three "extremely simple" rules: All kinds of conceptual things, they have names now that start with HTTP. If I take one of these HTTP names and I look it up I will get back some data in a standard format which is kind of useful data that somebody might like to know about that thing, about that event. When I get back that information it s not just got somebody s height and weight and when they were born, it s got relationships. And when it has relationships, whenever it expresses a relationship then the other thing that it s related to is given one of those names that starts with HTTP. 7

9 Linked Open Data (LOD) Linked Data that is Open (freely accessible) State of the LOD Cloud 2014 LOD Collections DataHub - large searchable collection of linked open data great for experimenting and research, formats: raw data, JSON, charts Local LOD Activities Data Brno #brno2050 Try eg. search for environmental resources in Brno: query=%c5%beivotn%c3%ad+prost%c5%99ed%c3%ad Schema.org Schema.org is a collaborative, community activity with a mission to create, maintain, and promote schemas for structured data on the Internet. Schema.org vocabulary can be used with many different encodings, including RDFa, Microdata JSON-LD. These vocabularies cover entities, relationships between entities and actions. Over 10 million sites use Schema.org to markup their content. Founded by Google, Microsoft, Yahoo, and Yandex, Schema.org vocabularies are developed by an open community process. see link: Ontologies What are ontologies? Instrument how to describe a knowledge. Set of terms and constructs and how they can be joint, derived etc. Basic categories of ontologies are: 8

10 Classes (general things) in the many domains of interest The relationships that can exist among things The properties (or attributes) those things may have Uses metadata frameworks (e.g.. RDF), but is better with more exact semantics. There are general frameworks for creation of specific ontologies. Use Cases Web portals - data integration on web. Multimedia collections. Large web sites management Design documentation Intelligent agents "Ubiquitous computation" XML Topic Maps An older activity (before RDF) The next proposal to WebOnt WG - 9