abstract objectType Entity

This is a base class to persistence. The entity attributes are generally set or updated by persistence implementations.

Members

name	type	mult	description
id	uuid		The id is a globally unique identifier (primary key) for an instance.
lastModified	ivoa:datetime	optional	The timestamp of last modification of this entity tracks changes in metadata and supports incremental operations. The timestamp is intended to be set and/or updated when the entity is stored (e.g. in a database).
metaChecksum	ivoa:anyURI	optional	This checksum of the metadata in this entity signals a change in the metadata of an instance and supports validation (e.g. to compare metadata before and after serialisation or persistence). A change in the metaChecksum can also be used to optimise operations like updating a row in the database only when the metaChecksum changed. A change in metaChecksum normally triggers a change in the lastModified timestamp. The URI must conform to the pattern {algorithm}:{hex value}, for example: \begin{verbatim}md5:4be91751541fd804e7207663a0822f56.\end{verbatim} The checksum of an entity is computed by accumulating byte representation of individual metadata values in the following order: (1) Entity.id for entities, (2) Entity.metaProducer, (3) state fields in alphabetic order (foo.a comes before foo.b) and using depth-first recursion (foo.abc.x comes before foo.def). The lastModified timestamp is not included in the metaChecksum calculation. Null values are ignored so that the addition of new fields in future versions will not change/invalidate existing checksums. Non-null values are converted to bytes as follows: \begin{itemize} \item string: UTF-8 encoded bytes \item URI: UTF-8 encoded bytes of the string representation \item VocabularyTerm: UTF-8 encoded bytes of the term (do not include the namespace) \item enumeration: the literal value converted to bytes \item float: IEEE754 single (4 bytes) \item double: IEEE754 double (8 bytes) \item boolean: convert to single byte, false=0, true=1 (1 byte) \item byte: as-is (1 byte) \item short: (2 bytes, network byte order == big endian)) \item integer: (4 bytes, network byte order == big endian) \item long: (8 bytes, network byte order == big endian) \item date: treat as a long (milliseconds since 1970-01-01 00:00:00 UTC) \end{itemize} TODO: truncatedDates=false, digestFieldNames=true, digestFieldnamesLowerCase=true TODO: external data model components: recursion or specify conversion above (interval, point, shape, multishape)
metaProducer	ivoa:anyURI	optional	This identifier is used to identify the tools used to produce the metadata. It also implicitly applies to child entities with null metaProducer. The form of the URI is not specified; implementations are free to use this to track metadata curation. For example, a pattern like {organisation}:{software name}-{version} is useful to support a variety of operational uses: query for metadata created by a version with a known bug or query for metadata created by an older version of the software and perform updates.