uk.ac.ic.doc.automed.qproc.cache
Class DefaultQueryCache

java.lang.Object
  uk.ac.ic.doc.automed.qproc.cache.DefaultQueryCache

All Implemented Interfaces:

java.util.Iterator, IQueryCache, Cacheable, Persistence, QueryRewritable

Direct Known Subclasses:

QueryCache

public class DefaultQueryCache
extends java.lang.Object
implements IQueryCache, Persistence, java.util.Iterator

Constructor Summary

protected

DefaultQueryCache(long ageTime) Creates a new instance of DefaultQueryCache (singleton)

Method Summary

void	addListener(CacheListener cacheListener) Register a listener for handling cache-related events
java.lang.String	addQuery(java.lang.String query, java.lang.Object metadata) Store reference to the AbstractQueryProcessor object that processes this query so that we can in a later stage use the query analysis with query result to build a semantic cache entry for the query .
void	addQueryResult(java.lang.String queryID, java.lang.Object resultObj) Add a new query to cache.
int	addSubQueryResult(java.lang.String queryID, java.lang.String subQuery, java.lang.Object resultObj) Add result of a sub-query of a query in the cache.
void	clear() Clear the cache
void	deserialise() Read content from disk (file or database)
java.util.List	getCachedQueries() Return external queries of all cached items
protected CacheContentDescription	getContent() Implements interface Cacheable.
CacheContentDescription	getContentObject() Return the cache data bag
ASG	getExactQuery(java.lang.String query) Check in the cache for an exact query match.
ASG	getExactSubQuery(java.lang.String subQuery) Check sub-query existence in the whole cache.
ASG	getExactSubQuery(java.lang.String queryID, java.lang.String subQuery) Check if result of the sub-query of a query already exists in the cache.
protected static DefaultQueryCache	getInstance(long ageTime) A singleton method to make sure that there is only one instance of query cache per peer
AbstractObjectBinding	getObjectBinding() Return an instance of object binding for serialisation
PersistentHandler	getPersistentHandler()
java.util.List	getQuery(ASG view)
ASG[]	getQuery(java.lang.String query) Check in the cache for a similar query match.
java.lang.Object[]	getQueryMetadataObjects() Return an array of metadata objects associated to the query objects
boolean	hasNext() Implements mandatory methods of the ListIterator interface
boolean	isEmpty()
java.lang.Object	next() Implements mandatory methods of the ListIterator interface Returns the metadata object of the next cache item
void	notifyListeners(Cacheable cacheObj) Notify listeners to handle a specific event
void	refresh() refresh cache
void	remove() Implements mandatory methods of the ListIterator interface
QueryRewriterResult	rewrite(ASG query, Schema querySchema, int type) Rewrite a query associated to a schema s using the local query cache
void	serialise(java.lang.Object obj) Save/synch a cache item object to disk (or database).
void	setPersistentHandler(PersistentHandler ph) Implement this method for serialising cache content

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DefaultQueryCache

protected DefaultQueryCache(long ageTime)

Creates a new instance of DefaultQueryCache (singleton)

Method Detail

getInstance

protected static DefaultQueryCache getInstance(long ageTime)

A singleton method to make sure that there is only one instance of query cache per peer

addQueryResult

public void addQueryResult(java.lang.String queryID,
                           java.lang.Object resultObj)
                    throws CacheIntegrityException

Add a new query to cache. The query is used as the key and result object
is the value. Often a query was pre-processed in query rewriting phase by an
instance of AbstractQueryProcessor whose result was added to this cache. Query result is often retrieved and later added to the cache at the execution phase
Hence, what we are doing here is to find the cache-item corresponding to the query and update it with

Specified by:

addQueryResult in interface IQueryCache

Parameters:

queryID - the unique query identifier (generated by #addQuery(String query, String fQuery, String sQuery, String iQuery, Object metadata, Object qproc) method

resultObj - the result object from query execution

Throws:

CacheIntegrityException

addSubQueryResult

public int addSubQueryResult(java.lang.String queryID,
                             java.lang.String subQuery,
                             java.lang.Object resultObj)
                      throws CacheIntegrityException

Add result of a sub-query of a query in the cache. A query might have one or more intermediate results each of which is added as a sub_result item (List object) of the query cache item.

Each query's sub result is represented as a two-dimensional array as follows:
Object[] subResult = new Object[] {subQuery, subQueryResult}

Specified by:

addSubQueryResult in interface IQueryCache

Parameters:

queryID - the id of the parent query

subQuery - sub-query string

resultObj - sub-query result object

Returns:

int the sub-result id of the query identified by queryID

Throws:

CacheIntegrityException

addQuery

public java.lang.String addQuery(java.lang.String query,
                                 java.lang.Object metadata)
                          throws CacheIntegrityException

Store reference to the AbstractQueryProcessor object that processes this query
so that we can in a later stage use the query analysis with query result
to build a semantic cache entry for the query
.
A query processor object is constructed for each query in query rewriting phase carried out by the query mediator component.

Specified by:

addQuery in interface IQueryCache

Parameters:

query - the original (external) IQL query posed by user

fQuery - the formulated query

sQuery - the executional representation of the query

iQuery - the internal representation of the query. This is the primary query id.

metadata - the metadata object of the query (e.g. QueryAnalyser)

qproc - the AbstractQueryProcessor object

Returns:

String the unique query identifier

Throws:

CacheIntegrityException

getExactQuery

public ASG getExactQuery(java.lang.String query)

Check in the cache for an exact query match. Note that this method operates on the internal IQL representation of the query which must only result in at most one matched entry. In any case, this method returns an array of the possible query results as ASGs.

Specified by:

getExactQuery in interface IQueryCache

Parameters:

query - the query string must be in internal format

Returns:

ASG[] array of possible query results found in the cache

getExactSubQuery

public ASG getExactSubQuery(java.lang.String queryID,
                            java.lang.String subQuery)
                     throws CacheIntegrityException

Check if result of the sub-query of a query already exists in the cache. This method only checks sub-query existence among sub-queries of a given query instead of all queries in the cache

Specified by:

getExactSubQuery in interface IQueryCache

Parameters:

queryID - the ID of query to which the sub-query is associated

subQuery - sub-query to search for

Returns:

ASG sub-query result (or null if sub-query is not found

Throws:

CacheIntegrityException

getExactSubQuery

public ASG getExactSubQuery(java.lang.String subQuery)

Check sub-query existence in the whole cache. This method is preferred to throws CacheIntegrityException

Specified by:

getExactSubQuery in interface IQueryCache

Parameters:

subQuery - sub-query to search for

Returns:

ASG sub-query result (or null if sub-query is not found

getQuery

public ASG[] getQuery(java.lang.String query)

Check in the cache for a similar query match. Note that this method operates on the external IQL representation of the query which could result in more than one exact matches in the cache. In any case, this method returns an array of the possible query results as ASGs.

Specified by:

getQuery in interface IQueryCache

Parameters:

query - the query string must be in external format

Returns:

ASG[] array of possible query results found in the cache

getQuery

public java.util.List getQuery(ASG view)

getCachedQueries

public java.util.List getCachedQueries()

Return external queries of all cached items

Specified by:

getCachedQueries in interface IQueryCache

Returns:

List a list of all metadata objects in the cache OR null
if no queries are found

getQueryMetadataObjects

public java.lang.Object[] getQueryMetadataObjects()

Return an array of metadata objects associated to the query objects

Specified by:

getQueryMetadataObjects in interface IQueryCache

getContent

protected CacheContentDescription getContent()

Implements interface Cacheable. Returns a List object of cache content. Each item in the list is
a HashMap object containing id, query, result and timestamp values
of each cached query.

getContentObject

public CacheContentDescription getContentObject()

Return the cache data bag

Specified by:

getContentObject in interface Cacheable

setPersistentHandler

public void setPersistentHandler(PersistentHandler ph)

Description copied from interface: Persistence

Implement this method for serialising cache content

Specified by:

setPersistentHandler in interface Persistence

getPersistentHandler

public PersistentHandler getPersistentHandler()

serialise

public void serialise(java.lang.Object obj)

Save/synch a cache item object to disk (or database).

Specified by:

serialise in interface Persistence

deserialise

public void deserialise()

Read content from disk (file or database)

Specified by:

deserialise in interface Persistence

getObjectBinding

public AbstractObjectBinding getObjectBinding()

Description copied from interface: Persistence

Return an instance of object binding for serialisation

Specified by:

getObjectBinding in interface Persistence

clear

public void clear()

Clear the cache

Specified by:

clear in interface Cacheable

refresh

public void refresh()

refresh cache

Specified by:

refresh in interface Cacheable

addListener

public void addListener(CacheListener cacheListener)

Register a listener for handling cache-related events

Specified by:

addListener in interface Cacheable

Parameters:

cacheListener - a CacheListener object to add

notifyListeners

public void notifyListeners(Cacheable cacheObj)

Notify listeners to handle a specific event

Specified by:

notifyListeners in interface Cacheable

Parameters:

cacheObj - the Cacheable object to be used by listener to handle event

hasNext

public boolean hasNext()

Implements mandatory methods of the ListIterator interface

Specified by:

hasNext in interface java.util.Iterator

next

public java.lang.Object next()

Implements mandatory methods of the ListIterator interface Returns the metadata object of the next cache item

Specified by:

next in interface java.util.Iterator

remove

public void remove()

Implements mandatory methods of the ListIterator interface

Specified by:

remove in interface java.util.Iterator

rewrite

public QueryRewriterResult rewrite(ASG query,
                                   Schema querySchema,
                                   int type)
                            throws QueryRewriterException

Rewrite a query associated to a schema s using the local query cache

Specified by:

rewrite in interface QueryRewritable

Parameters:

query - the ASG query

querySchema - the source schema over which query is executed

QueryAnalyser[] - an array of QueryAnalyser objects of the cached views

type - specifies the type of query rewriting algorithm used (QueryRewriteProcessor for list of types)

Returns:

QueryRewriterResult a result object that can be used to manipulate the rewriting results

Throws:

QueryRewriterException

isEmpty

public boolean isEmpty()