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## org.biojava.bibliography
Interface BibRefQuery

    public interface BibRefQuery

The interface BibRefQuery is a fundamental part of the Bibliographic Query Service. It allows searching for and retrieving citations from a bibliographic repository. The result of the query methods is again of type BibRefQuery which allows further to refine the query. When the caller is satisfied with the query results, the retrieval methods can be used to get either a list of citations (of type `BibRef`), or an XML document representing citations.

Squeezing all query and retrieval methods into one interface allows to build very flexible systems, both distributed (where the client and repository parts are executed on different computers) and stand-alone (both parts are linked together into one process).

For example, this picture shows a client linked together with a repository implementation. These two parts communicate entirely via BibRefQuery interface. Each of them can be replaced without changing the other one. |
In this example, a client uses BibRefQuery interface to communicate only with a local implementation of a distributed architecture (a CORBA communication protocol in this case). The repository implementation is similarly shielded by the same interface from the communication protocol layer. |
The last picture shows yet another example of a distributed architecture showing the parts which must be changed when a different communication protocol is used (the SOAP-HTTP in this case). Note that both the client and repository implementation remained untouched. |

### The implementation is advised to used the following constructor

        public NameOfAnImplementation (String[] args, Hashtable props) {...}

where both `args` and `props` contain implementation specific parameters and properties. However, some properties are more probable to be used - the suggested names for them are defined either in this interface or in the "sister" interface `BibRefSupport`.

The use of this constructor makes easier to load dynamically different implementations.

The methods of the BibRefQuery interface can be divided into three groups. The first group deals with connections to bibliographic repositories - here are methods `connect`, `disconnect`, `destroy`, `getCollectionId`, and `isReady`.

The second and the most interesting group contains the query methods. As mentioned above, these methods (mostly) return an another query collection which is again query-able. Here belong methods `find`, `findByAuthor`, `findById`, `query`, `getBibRefCount`, and `sort`.

The last group has methods for retrieving citations from the resulting query collection. The retrieval methods also allow to return citations not fully populated with all available attribute data (for example, the long abstracts can be asked for only later). Here belong methods `getAllBibRefs`, `getBibRefs`, `getAllIDs`, `getAllBibRefsAsXML`, `getBibRefsAsXML`, and `getBibRefAsXML`.

### Simple and Qualified Attribute Names

There are several places where method arguments represent attribute names:

- In query methods, such as `find`, a list of attributes that should be searched.
- The query results are citations represented as `BibRef` instances but not necessarily fully populated - they may contain only a subset of attributes, the excluded attribute lists used in several methods.
- The results may be ordered by one or more attributes (method `sort`).

Therefore, this interface defines several rules how to specify attribute names whenever they have to be expressed as strings. The existence of these rules will make the implementations interoperable. But, of course, they can be ignored if the interoperability is not an issue.

The following rules define how to create stringified names for individual attributes.

1. The best recommended practice is to find attribute names from a controlled vocabulary - see details in `BibRefSupport` interface.
2. The stringified names of attributes of class `BibRef` are equal to the member names of this class. For example, `identifier`, `type`, `title`, `authors`.
3. The stringified names of attributes of sub-classes derived from class `BibRef`, and of attributes of other classes, are also equal to the member names but additionally they must be qualified by the resource type using two underscores ( __ ). For example, `Book__isbn`, `JournalArticle__from_journal`, `Journal__name`.

   > The somewhat unusual double underscore is suggested here because in some query languages (where the stringified attribute names can be used as variables) is an underscore the only non-alphabetic character allowed for variables.

4. The qualification part of the stringified name (together with underscores) can be omitted if there is no ambiguity. For example, if an implementation does not use property name `isbn` anywhere else, the `Book__isbn` can be replaced by simple `isbn`.

   > Be aware, however, that dropping the qualifier may compromise extendibility because a caller that expects a unique attribute name may break if another citation type is added with the same attribute name.

5. The stringified names of the attributes from `dynamic properties` are equal to their property names, applying the rule about qualification as defined above. Thus, for example, an attribute `registry_number` hidden in member `BibRef.properties` will be stringified simply as `registry_number`, and an attribute `location` hidden in properties of a sub-class representing books will be stringified as `Book__location`.
6. The stringified names of the attributes from `dynamic properties` for instances without their own sub-class must be qualified (as described above) by the contents of their `BibRef.type`. For example, a citation can be of type `letter`, but there is no sub-class `Letter`. Therefore, an attribute `type` has value `letter`. This value is then used to create a qualified stringified name `letter__subject`.
7. The stringified names should be considered case-insensitive. Thus, `book__location` is the same as `Book__location`, and `journalarticle__issue` equals to `JournalArticle__issue`.

### Query Matching and Ordering Criteria

Several methods dealing with queries and sorting use a list of criteria. The criteria define how the matching or ordering should be done.

Each criterion is fully defined by an instance of `BiblioCriterion`. Such definitions can be obtained from a controlled vocabulary - see `BibRefSupport.getSupportedCriteria()`.

Because each criterion is uniquely identifiable by its name, the querying and sorting methods use only lists of criteria names, not lists of full criteria definitions.

### Excluded and Only-included attributes

Several methods use parameter with excluded attributes, or a parameter with only-included attributes. There are two different meanings and uses of such attributes lists.

The first meaning is used by the query methods. They return a new query collection. From the practical and performance reasons it may be sometimes useful to define in advance that the citations representing the resulting query collection do not need to contain all attributes. The excluded list of attribute names defines what attributes are not needed - typical use is to exclude abstracts which may be quite long. This, using the excluded list in the query method means that the resulting query collection will never have all attributes fully filled with data (unless, of course, the implementation ignores the excluded list).

The second meaning is for the retrieval methods. They return citations from a current query collection and can decide that only some attributes in the returned citations are filled with data (such parameter list is always named onlyAttrs). It may again mean that less data will be transferred but it is a post-act decision because the query collection has already all data and only does not return them now, but the next retrieval method (on the same collection) can retrieve them.

The both uses may be applied in different scenarios, and their efficiency is very dependent on the repository implementation. Sometimes the creation of a query collection already includes heavy data manipulation - therefore, the first usage may help with performance, But sometimes the resulting query collection is more or less a virtual collection and the real data transfer is applied only when the citations are being retrieved. In this case, the later scenario may be more efficient.

Since:
  1.3
Version:
  $Id: BibRefQuery.java 2812 2003-07-16 16:01:11Z mrp $
Author:
  Martin Senger, Matthew Pocock
See Also:
  `BibRef`, `BibRefSupport`, `BiblioCriterion`

Field Summary
`static String` | `PROP_CRITERIONS` A property name specifying a list of searching and ordering criteria names (type of the property value should be `String[]`).
`static String` | `PROP_EXCLUDED_ATTRS` A property name specifying a list of excluded attribute names (the type of the property value should be `String[]`).

Method Summary
`void` | `connect()` It creates a connection to a bibliographic repository, or/and it makes all necessary initialization steps needed for further communication.
`void` | `connect(byte[] collectionId)` It creates a connection to a bibliographic repository, or/and it makes all necessary initialization steps needed for further communication, and it makes the collection described by `collectionId` the current collection.
`void` | `destroy()` It frees all resources related to this query collection.
`void` | `disconnect()` It disconnects from the repository.
`BibRefQuery` | `find(String[] keywords, String[] attrs, Hashtable properties)` The easiest direct method for querying a repository.
`BibRefQuery` | `findByAuthor(BiblioProvider author, Hashtable properties)` This is a convenient method for a common query.
`BibRef` | `findById(String bibRefId)` This is a convenient method returning just one citation.
`BibRef` | `findById(String bibRefId, String[] onlyAttrs)` This is a convenient method returning just one citation, perhaps with a limited number of attributes.
`BibRef[]` | `getAllBibRefs()` It returns all citations from the current collection as a (possibly big) array.
`BibRef[]` | `getAllBibRefs(String[] onlyAttrs)` It returns all citations from the current collection as a (possibly big) array, perhaps with a limited number of attributes.
`InputStream` | `getAllBibRefsAsXML()` It returns all citations from the current collection as an XML stream.
`String[]` | `getAllIDs()` A convenient method returning just identifiers of all current citations.
`String` | `getBibRefAsXML(BibRef bibRef)` A convenient utility method converting a given citation to its XML representation.
`int` | `getBibRefCount()` It returns the number of citations in the current collection.
`Enumeration` | `getBibRefs()` It returns an enumeration of all citations from the current collection.
`Enumeration` | `getBibRefs(String[] onlyAttrs)` It returns an enumeration of all citations from the current collection, perhaps with a limited number of attributes.
`Enumeration` | `getBibRefsAsXML()` It returns an enumeration of all citations from the current collection.
`byte[]` | `getCollectionId()` It returns an identification of the current query collection.
`boolean` | `isReady()` It checks if the repository is available.
`BibRefQuery` | `query(String query, Hashtable properties)` It queries the current collection using a query language.
`BibRefQuery` | `sort(String[] orderedBy, Hashtable properties)` It sorts the current collection and returns another collection which is a sorted copy of the current collection.

Field Detail

### PROP_EXCLUDED_ATTRS

    static final String PROP_EXCLUDED_ATTRS

  A property name specifying a list of excluded attribute names (the type of the property value should be `String[]`).

  The list is used to define attributes which are not returned in the resulting citations (see discussion on excluded attributes).

  See Also:
    `find`, `query`, Constant Field Values

### PROP_CRITERIONS

    static final String PROP_CRITERIONS

  A property name specifying a list of searching and ordering criteria names (type of the property value should be `String[]`). See discussion on criteria.

  See Also:
    `find`, `query`, Constant Field Values

Method Detail

### getCollectionId

    byte[] getCollectionId()

  It returns an identification of the current query collection.

  At the beginning, the identification usually contain a bibliographic repository name or its contents description. But later, usually after `connect()` or after the first query, the identification may contain information rich enough to be able to re-create the whole collection (e.g. it can contain IDs of all records in the given collection).

  An implementation is not required to provide a persistent collection identification. However, if it does provide, it should also be able to accept the same identifier in the `connect` method, and to use it to re-create the same collection.

  Returns:
    an identification of the current collection (may be null)

### connect

    void connect()
                 throws BibRefException

  It creates a connection to a bibliographic repository, or/and it makes all necessary initialization steps needed for further communication.

  However, there should be no need to call this method explicitly, the other methods should do it automatically before they need something from the repository.

  Throws:
    `BibRefException` - if the connection cannot be established

### connect

    void connect(byte[] collectionId)
                 throws BibRefException

  It creates a connection to a bibliographic repository, or/and it makes all necessary initialization steps needed for further communication, and it makes the collection described by `collectionId` the current collection.

  Parameters:
    `collectionId` - a (usually persistent) token allowing to re-create a collection; the parameter is the same as an identifier returned earlier by method `getCollectionId()`
  Throws:
    `BibRefException` - if the connection cannot be established, or if the collection with the given ID cannot be re-created
  See Also:
    `connect without parameters`

### isReady

    boolean isReady()

  It checks if the repository is available. The semantic of availabledepends on the implementation.

  Returns:
    true if it is ready

### disconnect

    void disconnect()

  It disconnects from the repository.

  The caller can use this method to announce that the current query collection will not be needed soon. However, it may still be possible to connect to it later again.

  See Also:
    `destroy for more permanent action`

### destroy

    void destroy()
                 throws BibRefException

  It frees all resources related to this query collection.

  The caller explicitly announces no interest in the current query collection at all. The existence of two separate methods `disconnect()` and `destroy` allows more flexibility for cases where an implementation deals with, for example, temporary repositories.

  Throws:
    `BibRefException` - if the connection to the repository is broken
  See Also:
    `disconnect for less permanent action`

### find

    BibRefQuery find(String[] keywords,
                     String[] attrs,
                     Hashtable properties)
                     throws BibRefException

  The easiest direct method for querying a repository.

  It is modeled on examples of web-based searches: A caller can specify virtually anything in the list of keywords and the implementation tries to search for these in as many attributes as possible and reasonable, applying logical AND between them. However, a caller can also specifically limit the search only to attributes specified in the searched list.

  Note that there is no real query language used by this method, therefore, this method is not suitable for queries requiring logical operators (others than AND).

  The query result can be influenced by the additional properties:

  - Property `PROP_EXCLUDED_ATTRS` is of type `String[]` and contains list of attributes names which should not be included in the resulting query collection. See discussions on excluded attributes and on stringified attribute names,
  - Property `PROP_CRITERIONS` is also of type `String[]` and contains list of criteria names. The caller specifies here what criteria she wishes, and this method can change this property and return here the criteria really used for the query. See also discussion about criteria.

  Parameters:
    `keywords` - keyword or phrases that are being looked for
    `attrs` - attributes names that should be searched; if this list is empty the implementation should search all reasonable attributes
    `properties` - specify attributes excluded from the results and requested criteria for the query
  Returns:
    a new query (and query-able) collection
  Throws:
    `BibRefException` - if query failed (which can have many reasons :-)) (note that an empty result does not cause an exception)

### findByAuthor

    BibRefQuery findByAuthor(BiblioProvider author,
                             Hashtable properties)
                             throws BibRefException

  This is a convenient method for a common query.

  The search is done only for attributes having non empty values in parameter `author`. For example, a search for citations written by authors with surname `Doe` can be specified by sending an instance of `BiblioPerson` with `surname` filled with `Doe` and with other attributes empty. Or, a search for institution `EBI` can be specified by sending an instance of `BiblioOrganization` with `name` containing `EBI`.

  The query result can be influenced by the additional properties:

  - Property `PROP_EXCLUDED_ATTRS` is of type `String[]` and contains list of attributes names which should not be included in the resulting query collection. See discussions on excluded attributes and on stringified attribute names,
  - Property `PROP_CRITERIONS` is also of type `String[]` and contains list of criteria names. The caller specifies here what criteria she wishes, and this method can change this property and return here the criteria really used for the query. See also discussion about criteria.

  Parameters:
    `author` - contains one or more attributes that are being search for
    `properties` - specify attributes excluded from the results and requested criteria for the query
  Returns:
    a new query (and query-able) collection
  Throws:
    `BibRefException` - if query failed (which can have many reasons :-)) (note that an empty result does not cause an exception)
  See Also:
    `find`, `BiblioPerson`, `BiblioOrganisation`, `BiblioService`

### findById

    BibRef findById(String bibRefId)
                    throws BibRefException

  This is a convenient method returning just one citation.

  It queries the current collection in order to find and to retrieve a citation with the given identifier. It depends on the implementation what could be used as an identifier - see `BibRef.identifier`.

  Parameters:
    `bibRefId` - an identifier of a citation that is being looked for
  Returns:
    a found bibliographic reference (citation)
  Throws:
    `BibRefException` - if such citation was not found (or something else bad happened)
  See Also:
    `findById with limited returned attributes`

### findById

    BibRef findById(String bibRefId,
                    String[] onlyAttrs)
                    throws BibRefException

  This is a convenient method returning just one citation, perhaps with a limited number of attributes.

  It queries the current collection in order to find and to retrieve a citation with the given identifier. It depends on the implementation what could be used as an identifier - see `BibRef.identifier`.

  The returned citation will contain at least attributes whose names are specified by the parameter `onlyAttrs` (see discussion on only-included attributes.

  It is meant to provide more lightweight citation. The implementation may provide more attributes than specified in `onlyAttrs` (e.g. it is always recommended to include an attribute representing a unique identifier of the citation even if it is not asked for).

  Note that one can ask only for attributes that are available in the current collection. If the collection was already created without some attributes (using property `PROP_EXCLUDED_ATTRS`, e.g in method `find`) one cannot expect to get them even if they are asked for by the parameter `onlyAttrs`.

  Parameters:
    `bibRefId` - an identifier of a citation that is being looked for
    `onlyAttrs` - a list of attribute names; at least these attributes will be included in the returned citation
  Returns:
    a found bibliographic reference (citation)
  Throws:
    `BibRefException` - if such citation was not found (or something else bad happened)
  See Also:
    `findById`

### query

    BibRefQuery query(String query,
                      Hashtable properties)
                      throws BibRefException

  It queries the current collection using a query language.

  Use this method when the simple `find` method is not sufficient. For example, when more logical or relational operators are needed to express the query,

  This specification does not propose any specific query language to use (but may in the future). Roughly speaking, the query method takes a `query` string and passes it to the repository implementation, and if the implementation understands the query the world is saved.

  Again, the query result can be influenced by the additional properties:

  - Property `PROP_EXCLUDED_ATTRS` is of type `String[]` and contains list of attributes names which should not be included in the resulting query collection. See discussions on excluded attributes and on stringified attribute names,
  - Property `PROP_CRITERIONS` is also of type `String[]` and contains list of criteria names. The caller specifies here what criteria she wishes, and this method can change this property and return here the criteria really used for the query. See also discussion about criteria.

  Parameters:
    `query` - an expression in a query language
    `properties` - specify attributes excluded from the results and requested criteria for the query
  Returns:
    a new query (and query-able) collection
  Throws:
    `BibRefException` - if query failed (which can have many reasons :-)) (note that an empty result does not cause an exception)
  See Also:
    `find`

### getBibRefCount

    int getBibRefCount()
                       throws BibRefException

  It returns the number of citations in the current collection.

  Returns:
    the size of this collection
  Throws:
    `BibRefException` - if a connection with the repository is broken

### sort

    BibRefQuery sort(String[] orderedBy,
                     Hashtable properties)
                     throws BibRefException

  It sorts the current collection and returns another collection which is a sorted copy of the current collection.

  This is not strictly speaking a query method but it also returns a query collection.

  The sorting result can be influenced by an additional property `PROP_CRITERIONS` (of type `String[]`) containing a list of sorting criteria names. The caller specifies here what criteria she wishes, and this method can change this property and return here the criteria really used for sorting.

  Parameters:
    `orderedBy` - a list of attribute names that the collection should be sorted by
    `properties` - FIXME: docs & params out of sync
  Returns:
    a sorted collection
  Throws:
    `BibRefException` - if sorting failed (which may also happen when the collection is too large)

### getAllBibRefs

    BibRef[] getAllBibRefs()
                           throws BibRefException

  It returns all citations from the current collection as a (possibly big) array. Obviously, the repository implementation may limit the number of returned records.

  Some attributes may be missing (empty) if the property `PROP_EXCLUDED_ATTRS` was used for creating the current collection. See discussion on excluded attributes.

  Returns:
    all citations from the current collection
  Throws:
    `BibRefException` - if the collection is too large, or if the connection to the repository is broken
  See Also:
    `getAllBibRefs with limited returned attributes`

### getAllBibRefs

    BibRef[] getAllBibRefs(String[] onlyAttrs)
                           throws BibRefException

  It returns all citations from the current collection as a (possibly big) array, perhaps with a limited number of attributes.

  The returned citations will contain at least attributes whose names are specified by the parameter `onlyAttrs`. It is meant to provide more lightweight citations. The implementation may provide more attributes than specified in `onlyAttrs` (e.g. it may be always good to include an attribute representing a unique identifier of a citation even if it is not asked for). See discussion on only-included attributes.

  Note that one can ask only for attributes that are available in the current collection. If the collection was already created without some attributes (using property `PROP_EXCLUDED_ATTRS`, e.g in method `find`) one cannot expect to get them even if they are asked for by the parameter `onlyAttrs`.

  Parameters:
    `onlyAttrs` - attributes to attempt to include
  Returns:
    all citations from the current collection
  Throws:
    `BibRefException` - if the collection is too large, or if the connection to the repository is broken
  See Also:
    `getAllBibRefs with all attributes`, `getAllIDs`

### getAllIDs

    String[] getAllIDs()
                       throws BibRefException

  A convenient method returning just identifiers of all current citations.

  Returns:
    a list of all identifiers
  Throws:
    `BibRefException` - if the collection is too large, or if the connection to the repository is broken

### getBibRefs

    Enumeration getBibRefs()
                           throws BibRefException

  It returns an enumeration of all citations from the current collection. The type of elements in the enumeration is `BibRef` (or of its sub-classes).

  Some attributes may be missing (empty) if the property `PROP_EXCLUDED_ATTRS` was used for creating the current collection.

  Returns:
    an iterator over all citations
  Throws:
    `BibRefException` - if the connection to the repository is broken
  See Also:
    `getAllBibRefs`

### getBibRefs

    Enumeration getBibRefs(String[] onlyAttrs)
                           throws BibRefException

  It returns an enumeration of all citations from the current collection, perhaps with a limited number of attributes. The type of elements in the enumeration is `BibRef` (or of its sub-classes).

  The citations available through the enumeration will contain at least attributes whose names are specified by the parameter `onlyAttrs`. It is meant to provide more lightweight citations. The implementation may provide more attributes than specified in `onlyAttrs` (e.g. it may be always good to include an attribute representing a unique identifier of a citation even if it is not asked for).

  Note that one can ask only for attributes that are available in the current collection. If the collection was already created without some attributes (using property `PROP_EXCLUDED_ATTRS`, e.g in method `find`) one cannot expect to get them even if they are asked for by the parameter `onlyAttrs`.

  Parameters:
    `onlyAttrs` - attributes to attempt to fetch
  Returns:
    an iterator over all citations
  Throws:
    `BibRefException` - if the connection to the repository is broken
  See Also:
    `getAllBibRefs`, `getBibRefs with all attributes`

### getAllBibRefsAsXML

    InputStream getAllBibRefsAsXML()
                                   throws BibRefException

  It returns all citations from the current collection as an XML stream. The contents of such XML stream is widely repository dependent.

  Some attributes may be missing (empty) if the property `PROP_EXCLUDED_ATTRS` was used for creating the current collection.

  Returns:
    an XML data stream containing all citations from the current collection
  Throws:
    `BibRefException` - if the collection is too large, or if the connection to the repository is broken
  See Also:
    `getAllBibRefs`

### getBibRefsAsXML

    Enumeration getBibRefsAsXML()
                                throws BibRefException

  It returns an enumeration of all citations from the current collection. The type of elements in the enumeration is `String`. Each element represents one citation as an XML string. The contents of such XML string is widely repository dependent.

  Some attributes may be missing (empty) if the property `PROP_EXCLUDED_ATTRS` was used for creating the current collection.

  Returns:
    an iterator over all citations
  Throws:
    `BibRefException` - if the connection to the repository is broken
  See Also:
    `getBibRefs`, `getAllBibRefsAsXML`

### getBibRefAsXML

    String getBibRefAsXML(BibRef bibRef)
                          throws BibRefException

  A convenient utility method converting a given citation to its XML representation. It is useful, for example, in cases when a program annotates citations on-the-fly and needs them in the same XML format.

  The XML format depends on the repository where the citation comes from.

  Parameters:
    `bibRef` - a citation being converted into an XML format
  Returns:
    an XML representation of `bibRef`
  Throws:
    `BibRefException` - if the implementation needs it :-)

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