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| − | == SMILA Data Model ==
| + | #REDIRECT [[SMILA/Documentation/Data_Model_and_Serialization_Formats]] |
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| − | * Implementation bundle: <tt>org.eclipse.smila.datamodel</tt>
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| − | * Current Version: 0.8.0
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| − | === Concepts ===
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| − | The data to be processed in SMILA is represented as '''records'''. For example, one record could correspond to one document or to any resource which should be indexed or found in a search. A record consists of '''metadata''' and optional '''attachments'''.
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| − | [[Image:SMILA-datamodel-0.8.png|800px|SMILA data model version 0.8]]
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| − | * Metadata contains typed '''values''' (literals) arranged in '''maps''' (key-anything associations) and '''sequences''' (lists of anything). Values can be strings, long integers, double precision floating point numbers, booleans, dates (year, month, day) or datetimes (date + time of day, down to seconds). Maps and sequences can be nested arbitrarily, map keys are always strings. All metadata of one record is arranged in a single Map.
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| − | * Attachments can contain any binary content ("byte arrays"), possibly of larger size. During indexing they are not kept in memory all the time, but stored in a "binary storage" service and read only when actually needed.
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| − | A single entry in a record's metadata map is called '''Metadata element'''.
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| − | According to the use case, metadata elements can be semantically interpreted as:
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| − | ;Attributes: Usually, attributes are used when referring to the metadata of an object which is to be processed from a given data source or which is retrieved as the result of a search request. For example, typical attributes characterizing a web page to be indexed are its URL, the size in bytes, the MIME type, the title, and the plain-text content. These attributes are defined by the application domain.
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| − | ;Parameters: Attributes may not be adequate or sufficient for all record types. For example, in search processing, a record represents not a single object from some data source but rather a search request object. In such a case, the record's metadata does not contain attributes from the application domain on top-level but rather ''request parameters'' that configure and influence the request execution. These parameters are defined by the pipelets which are used in the workflow that was triggered by the search request. Also, their names do not start with underscores. However, a request or result record may contain application-specific attributes on deeper nested levels. Find an example, hopefully illustrating the difference between attributes and parameters, in [[SMILA/Documentation/2011.Simplification/Search|Search API]].
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| − | ;Annotations: An annotation can be used to add a data structure to the record which was generated as the result of some processing step. E.g., a named-entity-recognition pipelet could add an annotation describing at which character position some entity was found, meaning that the record was ''annotated'' with this additional information. If annotations appear in the same maps as attributes, their names should be chosen in such a way that they will not conflict with attribute names from the application, e.g. by prefixing them with an underscore "_".
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| − | ;System attributes: These attributes are needed by SMILA in order to coordinate the processing of a record (see below). Their names start with an underscore "_", so that they will not conflict with names from the application domain.
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| − | ==== System attributes ====
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| − | ;RecordID: A record must contain a single value string attributes named "_recordid" to identify the record. It must be unique for all processed records, this must be ensured by whoever initially created the record and submits it to the system (this would be crawlers or agents, usually). There is not predefined format of the record ID, it can contain any string, so creating UUIDs or something would be perfectly OK. Any information needed to access the original data the record was produced from should be placed by the producer in explicitly named attributes.
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| − | ;Source: A record should contain a second system attributes named "_source" containing the ID of the data source (e.g. crawler definition) that produced it. This is used by DeltaIndexing or RecordStorage to do operations on all records from one source.
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| − | === XML format ===
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| − | The XML format for a Record is designed to be quite compact:
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| − | <source lang="xml">
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| − | <Record xmlns="http://www.eclipse.org/smila/record" version="2.0">
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| − | <Val key="_recordid">web:http://example.org/something</Val>
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| − | <Val key="_source">web</Val>
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| − | <Val key="url">http://example.org/something</Val>
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| − | <Val key="filesize" type="long">1234</Val>
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| − | <Val key="sizeInKb" type="double">1.2</Val>
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| − | <Val key="checked" type="boolean">true</Val>
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| − | <Val key="created" type="date">2010-12-02</Val>
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| − | <Val key="lastModified" type="datetime">2010-12-02T16:20:54+01:00</Val>
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| − | <Seq key="trustee">
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| − | <Val>group1</Val>
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| − | <Val>group2</Val>
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| − | </Seq>
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| − | <Seq key="author">
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| − | <Map>
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| − | <Val key="firstname">John</Val>
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| − | <Val key="lastname">Doe</Val>
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| − | </Map>
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| − | <Map>
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| − | <Val key="firstname">Lisa</Val>
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| − | <Val key="lastname">Müller</Val>
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| − | </Map>
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| − | </Seq>
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| − | <Map key="contact">
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| − | <Val key="email">Homer.Simpson@powerplant.com</Val>
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| − | <Map key="adress">
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| − | <Val key="street">742 Evergreen Terrace</Val>
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| − | <Val key="city">Springfield</Val>
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| − | </Map>
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| − | </Map>
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| − | <Seq key="emptylist" />
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| − | <Map key="emptymap" />
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| − | <Attachment>content</Attachment>
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| − | <Attachment>fulltext</Attachment>
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| − | </Record>
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| − | </source>
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| − | Notes:
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| − | * The Any objects are represented by <Val>, <Map> and <Seq> elements.
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| − | * An object that is part of a map must have an additional "key" attribute. Elements of sequences must not have the "key" attribute.
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| − | * The value type is defined by a optional "type" attribute, the default is "string"
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| − | * The format of date values is "yyyy-MM-dd" (see [[http://download.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html Javadoc of SimpleDateFormat]] for meaning of the format string)
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| − | * The format of date values is "yyyy-MM-dd'T'HH:mm:ssZ", i.e. it must include timezone information.
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| − | * The top-level <Map> of an record is ommitted from the XML.
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| − | * In XML the record does not contain the attachment values, but only their names so that a reader knows that there are attachments to process.
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| − | === JSON format ===
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| − | Not yet implemented, but soon to come. Will look like this:
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| − | <source lang="javascript">
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| − | {
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| − | "_recordid" : "web:http://example.org/something",
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| − | "_source" : "web",
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| − | "filesize" : 1234,
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| − | "sizeInKb" : 1.2,
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| − | "checked" : true,
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| − | "created" : "2010-12-02",
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| − | "lastModified" : "2010-12-02T16:20:54+01:00",
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| − | "trustee" : [ "group1", "group2" ],
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| − | "author" :
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| − | [ {
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| − | "firstname" : "John",
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| − | "lastname" : "Doe"
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| − | },
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| − | {
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| − | "firstname" : "Lisa",
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| − | "lastname" : "Müller"
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| − | } ],
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| − | "contact" :
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| − | {
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| − | "email" : "Homer.Simpson@powerplant.com",
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| − | "adress" :
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| − | {
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| − | "street" : "742 Evergreen Terrace",
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| − | "city" : "Springfield"
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| − | }
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| − | },
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| − | "_attachments": ["content", "fulltext"]
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| − | }
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| − | </source>
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| − | Notes
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| − | * Value types are determined implicitly when parsing JSON:
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| − | ** if a number value can be parsed as a long integer, a long value will be created, else it will become a double value.
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| − | ** If a string (value enclosed in quotes) matches the date or datetime format a value of the respecive type will be created, else it will become a string value.
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| − | * Map keys are always strings and must be enclosed in quotes.
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| − | * Attachment names can be added as a system attribute "_attachments".
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| − | === Record Filters ===
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| − | '''Record Filters''' produce reduced copies of a record: A record filter has a name and contains a list of metadata element names. When applied to a record, it produces a copy of the record that contains only the elements of the list.
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| − | Record filters are described in a simple XML format:
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| − | <source lang="xml">
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| − | <RecordFilters>
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| − | <Filter name="filter0" />
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| − | <Filter name="filter1">
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| − | <Element name="attribute" />
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| − | </Filter>
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| − | <Filter name="filter3">
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| − | <Element name="attribute1" />
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| − | <Element name="attribute2" />
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| − | <Element name="attribute3" />
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| − | </Filter>
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| − | <Filter name="filter-all">
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| − | <Element name="*" />
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| − | </Filter>
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| − | </RecordFilters>
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| − | </source>
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| − | Notes:
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| − | * A filter always copies the system elements "_recordid" and "_source". Therefore the apparently empty "filter0" in this definition produces records that still contain these system elements.
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| − | * A filter may contain arbitrary numbers of element names. It's fine if an element does not appear in the record to copy, it's just ignored.
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| − | * A filter always removes attachments: The "filter-all" in this definition produces a copy of the record with all metadata elements, but not attachments.
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| − | Filters are usually applied by asking the Blackboard for a filtered copy of the record metadata. See Blackboard service API for details. To work with filters directly see package <tt>org.eclipse.smila.datamodel.filter</tt> for utility classes.
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| − | [[Category:SMILA]]
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