Schema Documentation {http://www.loc.gov/METS/}

METS: Metadata Encoding and Transmission Standard.
METS is intended to provide a standardized XML format for transmission of complex digital library objects between systems. As such, it can be seen as filling a role similar to that defined for the Submission Information Package (SIP), Archival Information Package (AIP) and Dissemination Information Package (DIP) in the Reference Model for an Open Archival Information System. The root element <mets> establishes the container for the information being stored and/or transmitted by the standard.

The mets header element <metsHdr> captures metadata about the METS document itself, not the digital object the METS document encodes. Although it records a more limited set of metadata, it is very similar in function and purpose to the headers employed in other schema such as the Text Encoding Initiative (TEI) or in the Encoded Archival Description (EAD).

agent:
The agent element <agent> provides for various parties and their roles with respect to the METS record to be documented.

The element <name> can be used to record the full name of the document agent.

The <note> element can be used to record any additional information regarding the agent's activities with respect to the METS document.

The alternative record identifier element <altRecordID> allows one to use alternative record identifier values for the digital object represented by the METS document; the primary record identifier is stored in the OBJID attribute in the root <mets> element.

A descriptive metadata section <dmdSec> records descriptive metadata pertaining to the METS object as a whole or one of its components. The <dmdSec> element conforms to same generic datatype as the <techMD>, <rightsMD>, <sourceMD> and <digiprovMD> elements, and supports the same sub-elements and attributes. A descriptive metadata element can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. METS allows multiple <dmdSec> elements; and descriptive metadata can be associated with any METS element that supports a DMDID attribute. Descriptive metadata can be expressed according to many current description standards (i.e., MARC, MODS, Dublin Core, TEI Header, EAD, VRA, FGDC, DDI) or a locally produced XML schema.

The administrative metadata section <amdSec> contains the administrative metadata pertaining to the digital object, its components and any original source material from which the digital object is derived. The <amdSec> is separated into four sub-sections that accommodate technical metadata (techMD), intellectual property rights (rightsMD), analog/digital source metadata (sourceMD), and digital provenance metadata (digiprovMD). Each of these subsections can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. Multiple instances of the <amdSec> element can occur within a METS document and multiple instances of its subsections can occur in one <amdSec> element. This allows considerable flexibility in the structuring of the administrative metadata. METS does not define a vocabulary or syntax for encoding administrative metadata. Administrative metadata can be expressed within the amdSec sub-elements according to many current community defined standards, or locally produced XML schemas.

The overall purpose of the content file section element <fileSec> is to provide an inventory of and the location for the content files that comprise the digital object being described in the METS document.

A sequence of file group elements <fileGrp> can be used group the digital files comprising the content of a METS object either into a flat arrangement or, because each file group element can itself contain one or more file group elements, into a nested (hierarchical) arrangement. In the case where the content files are images of different formats and resolutions, for example, one could group the image content files by format and create a separate <fileGrp> for each image format/resolution such as:
-- one <fileGrp> for the thumbnails of the images
-- one <fileGrp> for the higher resolution JPEGs of the image
-- one <fileGrp> for the master archival TIFFs of the images
For a text resource with a variety of content file types one might group the content files at the highest level by type, and then use the <fileGrp> element’s nesting capabilities to subdivide a <fileGrp> by format within the type, such as:
-- one <fileGrp> for all of the page images with nested <fileGrp> elements for each image format/resolution (tiff, jpeg, gif)
-- one <fileGrp> for a PDF version of all the pages of the document
-- one <fileGrp> for a TEI encoded XML version of the entire document or each of its pages.
A <fileGrp> may contain zero or more <fileGrp> elements and or <file> elements.

The structural map section <structMap> is the heart of a METS document. It provides a means for organizing the digital content represented by the <file> elements in the <fileSec> of the METS document into a coherent hierarchical structure. Such a hierarchical structure can be presented to users to facilitate their comprehension and navigation of the digital content. It can further be applied to any purpose requiring an understanding of the structural relationship of the content files or parts of the content files. The organization may be specified to any level of granularity (intellectual and or physical) that is desired. Since the <structMap> element is repeatable, more than one organization can be applied to the digital content represented by the METS document. The hierarchical structure specified by a <structMap> is encoded as a tree of nested <div> elements. A <div> element may directly point to content via child file pointer <fptr> elements (if the content is represented in the <fileSec<) or child METS pointer <mptr> elements (if the content is represented by an external METS document). The <fptr> element may point to a single whole <file> element that manifests its parent <div<, or to part of a <file> that manifests its <div<. It can also point to multiple files or parts of files that must be played/displayed either in sequence or in parallel to reveal its structural division. In addition to providing a means for organizing content, the <structMap> provides a mechanism for linking content at any hierarchical level with relevant descriptive and administrative metadata.

The structural link section element <structLink> allows for the specification of hyperlinks between the different components of a METS structure that are delineated in a structural map. This element is a container for a single, repeatable element, <smLink> which indicates a hyperlink between two nodes in the structural map. The <structLink> section in the METS document is identified using its XML ID attributes.

A behavior section element <behaviorSec> associates executable behaviors with content in the METS document by means of a repeatable behavior <behavior> element. This element has an interface definition <interfaceDef> element that represents an abstract definition of the set of behaviors represented by a particular behavior section. A <behavior> element also has a <mechanism> element which is used to point to a module of executable code that implements and runs the behavior defined by the interface definition. The <behaviorSec> element, which is repeatable as well as nestable, can be used to group individual behaviors within the structure of the METS document. Such grouping can be useful for organizing families of behaviors together or to indicate other relationships between particular behaviors.

A technical metadata element <techMD> records technical metadata about a component of the METS object, such as a digital content file. The <techMD> element conforms to same generic datatype as the <dmdSec>, <rightsMD>, <sourceMD> and <digiprovMD> elements, and supports the same sub-elements and attributes. A technical metadata element can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. METS allows multiple <techMD> elements; and technical metadata can be associated with any METS element that supports an ADMID attribute. Technical metadata can be expressed according to many current technical description standards (such as MIX and textMD) or a locally produced XML schema.

An intellectual property rights metadata element <rightsMD> records information about copyright and licensing pertaining to a component of the METS object. The <rightsMD> element conforms to same generic datatype as the <dmdSec>, <techMD>, <sourceMD> and <digiprovMD> elements, and supports the same sub-elements and attributes. A rights metadata element can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. METS allows multiple <rightsMD> elements; and rights metadata can be associated with any METS element that supports an ADMID attribute. Rights metadata can be expressed according current rights description standards (such as CopyrightMD and rightsDeclarationMD) or a locally produced XML schema.

A source metadata element <sourceMD> records descriptive and administrative metadata about the source format or media of a component of the METS object such as a digital content file. It is often used for discovery, data administration or preservation of the digital object. The <sourceMD> element conforms to same generic datatype as the <dmdSec>, <techMD>, <rightsMD>, and <digiprovMD> elements, and supports the same sub-elements and attributes. A source metadata element can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. METS allows multiple <sourceMD> elements; and source metadata can be associated with any METS element that supports an ADMID attribute. Source metadata can be expressed according to current source description standards (such as PREMIS) or a locally produced XML schema.

A digital provenance metadata element <digiprovMD> can be used to record any preservation-related actions taken on the various files which comprise a digital object (e.g., those subsequent to the initial digitization of the files such as transformation or migrations) or, in the case of born digital materials, the files’ creation. In short, digital provenance should be used to record information that allows both archival/library staff and scholars to understand what modifications have been made to a digital object and/or its constituent parts during its life cycle. This information can then be used to judge how those processes might have altered or corrupted the object’s ability to accurately represent the original item. One might, for example, record master derivative relationships and the process by which those derivations have been created. Or the <digiprovMD> element could contain information regarding the migration/transformation of a file from its original digitization (e.g., OCR, TEI, etc.,)to its current incarnation as a digital object (e.g., JPEG2000). The <digiprovMD> element conforms to same generic datatype as the <dmdSec>, <techMD>, <rightsMD>, and <sourceMD> elements, and supports the same sub-elements and attributes. A digital provenance metadata element can either wrap the metadata (mdWrap) or reference it in an external location (mdRef) or both. METS allows multiple <digiprovMD> elements; and digital provenance metadata can be associated with any METS element that supports an ADMID attribute. Digital provenance metadata can be expressed according to current digital provenance description standards (such as PREMIS) or a locally produced XML schema.

The file element <file> provides access to the content files for the digital object being described by the METS document. A <file> element may contain one or more <FLocat> elements which provide pointers to a content file and/or a <FContent> element which wraps an encoded version of the file. Embedding files using <FContent> can be a valuable feature for exchanging digital objects between repositories or for archiving versions of digital objects for off-site storage. All <FLocat> and <FContent> elements should identify and/or contain identical copies of a single file. The <file> element is recursive, thus allowing sub-files or component files of a larger file to be listed in the inventory. Alternatively, by using the <stream> element, a smaller component of a file or of a related file can be placed within a <file> element. Finally, by using the <transformFile> element, it is possible to include within a <file> element a different version of a file that has undergone a transformation for some reason, such as format migration.

The structural divisions of the hierarchical organization provided by a <structMap> are represented by division <div> elements, which can be nested to any depth. Each <div> element can represent either an intellectual (logical) division or a physical division. Every <div> node in the structural map hierarchy may be connected (via subsidiary <mptr> or <fptr> elements) to content files which represent that div's portion of the whole document.

Like the <fptr> element, the METS pointer element <mptr> represents digital content that manifests its parent <div> element. Unlike the <fptr>, which either directly or indirectly points to content represented in the <fileSec> of the parent METS document, the <mptr> element points to content represented by an external METS document. Thus, this element allows multiple discrete and separate METS documents to be organized at a higher level by a separate METS document. For example, METS documents representing the individual issues in the series of a journal could be grouped together and organized by a higher level METS document that represents the entire journal series. Each of the <div> elements in the <structMap> of the METS document representing the journal series would point to a METS document representing an issue. It would do so via a child <mptr> element. Thus the <mptr> element gives METS users considerable flexibility in managing the depth of the <structMap> hierarchy of individual METS documents. The <mptr> element points to an external METS document by means of an xlink:href attribute and associated XLink attributes.

The <fptr> or file pointer element represents digital content that manifests its parent <div> element. The content represented by an <fptr> element must consist of integral files or parts of files that are represented by <file> elements in the <fileSec>. Via its FILEID attribute, an <fptr> may point directly to a single integral <file> element that manifests a structural division. However, an <fptr> element may also govern an <area> element, a <par>, or a <seq> which in turn would point to the relevant file or files. A child <area> element can point to part of a <file> that manifests a division, while the <par> and <seq> elements can point to multiple files or parts of files that together manifest a division. More than one <fptr> element can be associated with a <div> element. Typically sibling <fptr> elements represent alternative versions, or manifestations, of the same content

The <par> or parallel files element aggregates pointers to files, parts of files, and/or sequences of files or parts of files that must be played or displayed simultaneously to manifest a block of digital content represented by an <fptr> element. This might be the case, for example, with multi-media content, where a still image might have an accompanying audio track that comments on the still image. In this case, a <par> element would aggregate two <area> elements, one of which pointed to the image file and one of which pointed to the audio file that must be played in conjunction with the image. The <area> element associated with the image could be further qualified with SHAPE and COORDS attributes if only a portion of the image file was pertinent and the <area> element associated with the audio file could be further qualified with BETYPE, BEGIN, EXTTYPE, and EXTENT attributes if only a portion of the associated audio file should be played in conjunction with the image.

The sequence of files element <seq> aggregates pointers to files, parts of files and/or parallel sets of files or parts of files that must be played or displayed sequentially to manifest a block of digital content. This might be the case, for example, if the parent <div> element represented a logical division, such as a diary entry, that spanned multiple pages of a diary and, hence, multiple page image files. In this case, a <seq> element would aggregate multiple, sequentially arranged <area> elements, each of which pointed to one of the image files that must be presented sequentially to manifest the entire diary entry. If the diary entry started in the middle of a page, then the first <area> element (representing the page on which the diary entry starts) might be further qualified, via its SHAPE and COORDS attributes, to specify the specific, pertinent area of the associated image file.

The area element <area> typically points to content consisting of just a portion or area of a file represented by a <file> element in the <fileSec>. In some contexts, however, the <area> element can also point to content represented by an integral file. A single <area> element would appear as the direct child of a <fptr> element when only a portion of a <file>, rather than an integral <file>, manifested the digital content represented by the <fptr>. Multiple <area> elements would appear as the direct children of a <par> element or a <seq> element when multiple files or parts of files manifested the digital content represented by an <fptr> element. When used in the context of a <par> or <seq> element an <area> element can point either to an integral file or to a segment of a file as necessary.

The Structural Map Link element <smLink> identifies a hyperlink between two nodes in the structural map. You would use <smLink>, for instance, to note the existence of hypertext links between web pages, if you wished to record those links within METS. NOTE: <smLink> is an empty element. The location of the <smLink> element to which the <smLink> element is pointing MUST be stored in the xlink:href attribute.

The structMap link group element <smLinkGrp> provides an implementation of xlink:extendLink, and provides xlink compliant mechanisms for establishing xlink:arcLink type links between 2 or more <div> elements in <structMap> element(s) occurring within the same METS document or different METS documents. The smLinkGrp could be used as an alternative to the <smLink> element to establish a one-to-one link between <div> elements in the same METS document in a fully xlink compliant manner. However, it can also be used to establish one-to-many or many-to-many links between <div> elements. For example, if a METS document contains two <structMap> elements, one of which represents a purely logical structure and one of which represents a purely physical structure, the <smLinkGrp> element would provide a means of mapping a <div> representing a logical entity (for example, a newspaper article) with multiple <div> elements in the physical <structMap> representing the physical areas that together comprise the logical entity (for example, the <div> elements representing the page areas that together comprise the newspaper article).

The structMap locator link element <smLocatorLink> is of xlink:type "locator". It provides a means of identifying a <div> element that will participate in one or more of the links specified by means of <smArcLink> elements within the same <smLinkGrp>. The participating <div> element that is represented by the <smLocatorLink> is identified by means of a URI in the associate xlink:href attribute. The lowest level of this xlink:href URI value should be a fragment identifier that references the ID value that identifies the relevant <div> element. For example, "xlink:href='#div20'" where "div20" is the ID value that identifies the pertinent <div> in the current METS document. Although not required by the xlink specification, an <smLocatorLink> element will typically include an xlink:label attribute in this context, as the <smArcLink> elements will reference these labels to establish the from and to sides of each arc link.

A behavior element <behavior> can be used to associate executable behaviors with content in the METS document. This element has an interface definition <interfaceDef> element that represents an abstract definition of a set of behaviors represented by a particular behavior. A <behavior> element also has a behavior mechanism <mechanism> element, a module of executable code that implements and runs the behavior defined abstractly by the interface definition.

The interface definition <interfaceDef> element contains a pointer to an abstract definition of a single behavior or a set of related behaviors that are associated with the content of a METS object. The interface definition object to which the <interfaceDef> element points using xlink:href could be another digital object, or some other entity, such as a text file which describes the interface or a Web Services Description Language (WSDL) file. Ideally, an interface definition object contains metadata that describes a set of behaviors or methods. It may also contain files that describe the intended usage of the behaviors, and possibly files that represent different expressions of the interface definition.

A mechanism element <mechanism> contains a pointer to an executable code module that implements a set of behaviors defined by an interface definition. The <mechanism> element will be a pointer to another object (a mechanism object). A mechanism object could be another METS object, or some other entity (e.g., a WSDL file). A mechanism object should contain executable code, pointers to executable code, or specifications for binding to network services (e.g., web services).

The metadata reference element <mdRef> element is a generic element used throughout the METS schema to provide a pointer to metadata which resides outside the METS document. NB: <mdRef> is an empty element. The location of the metadata must be recorded in the xlink:href attribute, supplemented by the XPTR attribute as needed.

A metadata wrapper element <mdWrap> provides a wrapper around metadata embedded within a METS document. The element is repeatable. Such metadata can be in one of two forms: 1) XML-encoded metadata, with the XML-encoding identifying itself as belonging to a namespace other than the METS document namespace. 2) Any arbitrary binary or textual form, PROVIDED that the metadata is Base64 encoded and wrapped in a <binData> element within the internal descriptive metadata element.

The binary data wrapper element <binData> is used to contain Base64 encoded metadata.

The xml data wrapper element <xmlData> is used to contain XML encoded metadata. The content of an <xmlData> element can be in any namespace or in no namespace. As permitted by the XML Schema Standard, the processContents attribute value for the metadata in an <xmlData> is set to “lax”. Therefore, if the source schema and its location are identified by means of an XML schemaLocation attribute, then an XML processor will validate the elements for which it can find declarations. If a source schema is not identified, or cannot be found at the specified schemaLocation, then an XML validator will check for well-formedness, but otherwise skip over the elements appearing in the <xmlData> element.

The file location element <FLocat> provides a pointer to the location of a content file. It uses the XLink reference syntax to provide linking information indicating the actual location of the content file, along with other attributes specifying additional linking information. NOTE: <FLocat> is an empty element. The location of the resource pointed to MUST be stored in the xlink:href attribute.

The file content element <FContent> is used to identify a content file contained internally within a METS document. The content file must be either Base64 encoded and contained within the subsidiary <binData> wrapper element, or consist of XML information and be contained within the subsidiary <xmlData> wrapper element.

A binary data wrapper element <binData> is used to contain a Base64 encoded file.

An xml data wrapper element <xmlData> is used to contain an XML encoded file. The content of an <xmlData> element can be in any namespace or in no namespace. As permitted by the XML Schema Standard, the processContents attribute value for the metadata in an <xmlData> element is set to “lax”. Therefore, if the source schema and its location are identified by means of an xsi:schemaLocation attribute, then an XML processor will validate the elements for which it can find declarations. If a source schema is not identified, or cannot be found at the specified schemaLocation, then an XML validator will check for well-formedness, but otherwise skip over the elements appearing in the <xmlData> element.

A component byte stream element <stream> may be composed of one or more subsidiary streams. An MPEG4 file, for example, might contain separate audio and video streams, each of which is associated with technical metadata. The repeatable <stream> element provides a mechanism to record the existence of separate data streams within a particular file, and the opportunity to associate <dmdSec> and <amdSec> with those subsidiary data streams if desired.

The transform file element <transformFile> provides a means to access any subsidiary files listed below a <file> element by indicating the steps required to "unpack" or transform the subsidiary files. This element is repeatable and might provide a link to a <behavior> in the <behaviorSec> that performs the transformation.