com.bigdata.gom.gpo

Class GPO

java.lang.Object

com.bigdata.gom.gpo.GPO

All Implemented Interfaces:

IGenericSkin, IGPO

public class GPO
extends Object
implements IGPO

A TripleStore backed GPO yields a number of challenges.

1. We need a property mechanism to track the statement assertion and retractions required for efficient update. The GPOEntry class provides support for this with its linked lists of GPOValues, also supporting multiple values per predicate.
2. A strategy for lazy materialization. This turns out to be fairly straightforward, with the GPO created unmaterialized and requesting as necessary
3. Most importantly we have a consistency/referential integrity issue since the GPO state is not kept in sync with the underlying triple store. The simple solution is to ensure that any update is immediately pushed through to the underlying store, but this loses the advantage of the localised cache. Although it could be argued that a general query is made against committed data the same case cannot be made when building GPO models. It seems we need a mechanism to lazily flush updates relevant to a specific property.
4. An alternate solution is to view the ObjectManager transactions as transactional updates to the GPO structures and that when these are committed then the model is consistent. Separating the GPO commit from any underlying TripleStore commit. So the GPO processing inside the GPO transaction is restricted and referential integrity is not maintained. This is similar to the read-committed query semantics of most databases, which is not to commend it in any way. I am keen to find a solution to this.
5. One option is to force GPO related updates through to the underlying store, not necessarily a problem since a rollback already performs a TripleStore abort anyhow.

Author:

Martyn Cutcher

Constructor Summary

Constructors

Constructor and Description
GPO(IObjectManager om, org.openrdf.model.BNode id, org.openrdf.model.Statement stmt)
GPO(IObjectManager om, org.openrdf.model.Resource id)

Method Summary

Methods

Modifier and Type	Method and Description
void	addValue(org.openrdf.model.URI property, org.openrdf.model.Value value) Assert (self,p,newValue).
IGenericSkin	asClass(Class theClassOrInterface) Returns an transient object that wraps the same persistent object but exposes the behavior identified by the identified interface.
IGPO	asGeneric() This method returns the eventual delegate that implements the IGPO interface and is primarily used to peel off a skin and gain access to implementation specific methods on the IGPO implementation object.
void	dematerialize()
void	doCommit() Called by the ObjectManager when flushing dirty objects.
String	encode(org.openrdf.model.Resource v) Encode a URL, Literal, or blank node for inclusion in a SPARQL query to be sent to the remote service.
BigdataResource	getId() Returns the persistent identity of the generic object.
IGPO	getLink(org.openrdf.model.URI property, IGPO target) Return the IGPO modeling the link iff it exists.
Set<IGPO>	getLinksIn() getLinksIn simply filters the values for Resources and returns a wrapper.
ILinkSet	getLinksIn(org.openrdf.model.URI property) All ?y where (?y,p,self).
Set<IGPO>	getLinksOut() All ?y where (self,?,?y).
ILinkSet	getLinksOut(org.openrdf.model.URI property) All ?y where (self,p,?y).
IObjectManager	getObjectManager() Return the IObjectManager used to materialize or create this generic object.
Iterator<org.openrdf.model.URI>	getPropertyURIs()
Map<org.openrdf.model.URI,Long>	getReverseLinkProperties() Return a map giving the range count for each reverse link property.
IGenericSkin	getSkin(Class intf) The getSkin method is inspired somewhat by the Microsoft Win32 getInterface that allowed an object to return multiple interfaces.
BigdataStatement	getStatement() Iff this IGPO represents a statement (aka link), then return that Statement.
Set<org.openrdf.model.Statement>	getStatements() All (self,?p,?o).
IGPO	getType() FIXME: this method will be moved to an as yet unnamed derived class that will become the superclass for alchemist generated subclasses.
org.openrdf.model.Value	getValue(org.openrdf.model.URI property) Return first Value for property or null if no Value for that property.
Set<org.openrdf.model.Value>	getValues(org.openrdf.model.URI property) All ?y where (self,p,?y).
int	hashCode() Return the hash code of the identity of the generic object.
void	initLinkValue(org.openrdf.model.URI predicate, org.openrdf.model.Resource object)
void	initValue(org.openrdf.model.URI predicate, org.openrdf.model.Value object)
boolean	isBound(org.openrdf.model.URI property) Exists (self,p,?y).
boolean	isDirty()
boolean	isMemberOf(ILinkSet linkSet) Exists (?x,linkSet.property,self).
IGPO	materialize() Basis for lazy materialization, checks materialize state and if false requests matierialization from the ObjectManager
String	pp()
void	prepareBatchUpdate(List<org.openrdf.model.Statement> insertList, List<org.openrdf.model.Statement> removeList) Adds statements to be inserted and removed to the appropriate lists based on the GPOs internal edit set.
void	remove() FIXME This should run a query (unless it is fully materialized, including the reverse links and forward links) and build an edit list for the retracts.
void	removeValue(org.openrdf.model.URI property, org.openrdf.model.Value value) Remove (self,p,oldValue) if found.
void	removeValues(org.openrdf.model.URI property) Remove all (self,p,?).
void	setMaterialized(boolean b)
void	setValue(org.openrdf.model.URI property, org.openrdf.model.Value newValue) Replace (self,p,?x) with (self,p,newValue).

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.bigdata.gom.gpo.IGPO

equals

Constructor Detail

GPO

public GPO(IObjectManager om,
   org.openrdf.model.Resource id)

GPO

public GPO(IObjectManager om,
   org.openrdf.model.BNode id,
   org.openrdf.model.Statement stmt)

Method Detail

dematerialize

public void dematerialize()

hashCode

public int hashCode()

Description copied from interface: IGPO

Return the hash code of the identity of the generic object. (The hash code is NOT based on the internal state of the generic object.)

Specified by:

hashCode in interface IGPO

Overrides:

hashCode in class Object

asClass

public IGenericSkin asClass(Class theClassOrInterface)

Description copied from interface: IGPO

Returns an transient object that wraps the same persistent object but exposes the behavior identified by the identified interface. The interface effectively names the behavior that will be wrapped around the persistent data. If the current object already implements the desired interface, then it is simply returned. If a suitable IGenericSkin has already been minted for this generic object, then it is simply returned. Otherwise an implementation class for the interface MUST have been registered with the runtime and MUST implement a constructor accepting a single IGenericSkin argument.

The life cycle of a skin object returned by this method MUST be no less than the in-memory life cycle of the generic object for which the skin was minted. This constraint makes it possible to have transient yet expensive initialization, such as caches, on skin objects.

Specified by:

asClass in interface IGPO

Returns:

An object that wraps the same persistent data but implements the desired interface.

See Also:

IGenericSkin, GenericSkinRegistry

getObjectManager

public IObjectManager getObjectManager()

Description copied from interface: IGPO

Return the IObjectManager used to materialize or create this generic object.

Specified by:

getObjectManager in interface IGPO

getId

public BigdataResource getId()

Description copied from interface: IGPO

Returns the persistent identity of the generic object.

Specified by:

getId in interface IGPO

getStatement

public BigdataStatement getStatement()

Iff this IGPO represents a statement (aka link), then return that Statement.

Returns:

The Statement or null if the IGPO does not represent a Statement.

encode

public String encode(org.openrdf.model.Resource v)

Encode a URL, Literal, or blank node for inclusion in a SPARQL query to be sent to the remote service.

Parameters:

v - The resource.

Returns:

The encoded representation of the resource.

See Also:

ObjectMgrModel.encode(Resource)

getLinksIn

public Set<IGPO> getLinksIn()

getLinksIn simply filters the values for Resources and returns a wrapper.

Specified by:

getLinksIn in interface IGPO

getLinksIn

public ILinkSet getLinksIn(org.openrdf.model.URI property)

All ?y where (?y,p,self).

Specified by:

getLinksIn in interface IGPO

getLinksOut

public Set<IGPO> getLinksOut()

All ?y where (self,?,?y).

Specified by:

getLinksOut in interface IGPO

getLinksOut

public ILinkSet getLinksOut(org.openrdf.model.URI property)

All ?y where (self,p,?y).

Specified by:

getLinksOut in interface IGPO

getReverseLinkProperties

public Map<org.openrdf.model.URI,Long> getReverseLinkProperties()

Description copied from interface: IGPO

Return a map giving the range count for each reverse link property.

 SELECT ?p, COUNT(*) WHERE { ?o ?p  } GROUP BY ?p
 

Specified by:

getReverseLinkProperties in interface IGPO

getStatements

public Set<org.openrdf.model.Statement> getStatements()

Description copied from interface: IGPO

All (self,?p,?o).

Specified by:

getStatements in interface IGPO

getValue

public org.openrdf.model.Value getValue(org.openrdf.model.URI property)

Description copied from interface: IGPO

Return first Value for property or null if no Value for that property.

Specified by:

getValue in interface IGPO

getValues

public Set<org.openrdf.model.Value> getValues(org.openrdf.model.URI property)

Description copied from interface: IGPO

All ?y where (self,p,?y).

Specified by:

getValues in interface IGPO

isBound

public boolean isBound(org.openrdf.model.URI property)

Description copied from interface: IGPO

Exists (self,p,?y).

Specified by:

isBound in interface IGPO

isMemberOf

public boolean isMemberOf(ILinkSet linkSet)

Description copied from interface: IGPO

Exists (?x,linkSet.property,self).

Specified by:

isMemberOf in interface IGPO

remove

public void remove()

FIXME This should run a query (unless it is fully materialized, including the reverse links and forward links) and build an edit list for the retracts. [There could be a separate operation to remove only those properties associated with a skin.]

Specified by:

remove in interface IGPO

initValue

public void initValue(org.openrdf.model.URI predicate,
             org.openrdf.model.Value object)

initLinkValue

public void initLinkValue(org.openrdf.model.URI predicate,
                 org.openrdf.model.Resource object)

setValue

public void setValue(org.openrdf.model.URI property,
            org.openrdf.model.Value newValue)

Description copied from interface: IGPO

Replace (self,p,?x) with (self,p,newValue).

Specified by:

setValue in interface IGPO

getLink

public IGPO getLink(org.openrdf.model.URI property,
           IGPO target)

Return the IGPO modeling the link iff it exists. FIXME This should be conditional, returning null if the link does not exist. However, that conditional test needs to be efficient.

Specified by:

getLink in interface IGPO

addValue

public void addValue(org.openrdf.model.URI property,
            org.openrdf.model.Value value)

Description copied from interface: IGPO

Assert (self,p,newValue).

Specified by:

addValue in interface IGPO

removeValue

public void removeValue(org.openrdf.model.URI property,
               org.openrdf.model.Value value)

Description copied from interface: IGPO

Remove (self,p,oldValue) if found.

Specified by:

removeValue in interface IGPO

removeValues

public void removeValues(org.openrdf.model.URI property)

Description copied from interface: IGPO

Remove all (self,p,?).

Specified by:

removeValues in interface IGPO

isDirty

public boolean isDirty()

asGeneric

public IGPO asGeneric()

Description copied from interface: IGenericSkin

This method returns the eventual delegate that implements the IGPO interface and is primarily used to peel off a skin and gain access to implementation specific methods on the IGPO implementation object. When invoked on an object that directly implements the IGPO behavior (vs delegating the interface to an implementation object), then that object is returned. The return value is never null.

Specified by:

asGeneric in interface IGenericSkin

pp

public String pp()

Specified by:

pp in interface IGPO

Returns:

a pretty printed representation of the GPO

getType

public IGPO getType()

Description copied from interface: IGPO

FIXME: this method will be moved to an as yet unnamed derived class that will become the superclass for alchemist generated subclasses.

Specified by:

getType in interface IGPO

doCommit

public void doCommit()

Called by the ObjectManager when flushing dirty objects. This can occur incrementally or on ObjectManager commit. The object is marked as clean once written.

materialize

public IGPO materialize()

Basis for lazy materialization, checks materialize state and if false requests matierialization from the ObjectManager

Specified by:

materialize in interface IGPO

Returns:

This IGPO.

setMaterialized

public void setMaterialized(boolean b)

prepareBatchUpdate

public void prepareBatchUpdate(List<org.openrdf.model.Statement> insertList,
                      List<org.openrdf.model.Statement> removeList)

Adds statements to be inserted and removed to the appropriate lists based on the GPOs internal edit set.

Parameters:

insertList - The list of statements to be added.

removeList - The list of statements to be removed.

getSkin

public IGenericSkin getSkin(Class intf)

The getSkin method is inspired somewhat by the Microsoft Win32 getInterface that allowed an object to return multiple interfaces. The difference with the GPO skin is that the skin should be able to interact with any underlying GPO object.

It may be worthwhile performance wise to cache a skin. I believe of more importance is to preserve identity - even of the interface/skin object.

Parameters:

skin - interface required

Returns:

a skin if available

getPropertyURIs

public Iterator<org.openrdf.model.URI> getPropertyURIs()