as described above , the present invention is characterized by the use of an unchanged reference handle . that is , in accordance with the present invention , a value of the reference handle that the oma service uses to utilize the shared uri list stored in the shared xdms is a static value that remains unchanged after the referred element is created and before the reference handle vanishes . when a static reference handle is used , the relationships between a change in referred objects , i . e ., the & lt ; list & gt ; element and the & lt ; entry & gt ; element , and referring objects , i . e ., the & lt ; external & gt ; element , the & lt ; resource - list & gt ; element , and the & lt ; entry - ref & gt ; element , are independent . accordingly , an internal change in the referred objects does not affect the reference relationship with the referring objects . while a reference handle used in the present invention can be created by several methods , the following description will focus primarily on a representative method of creating a reference handle , wherein a system managing a shared uri list uses a random value which is automatically created in response to a user &# 39 ; s request . the present invention may be implemented using a conventional oma presence architecture as illustrated in fig1 . tables 8 and 9 illustrate a ( single ) definition of enhanced xml schema of resource - list in table 1 and 2 , according to the present invention . more specifically , tables 8 and 9 show a definition of xml schema for using a random value as a reference handle . as shown in tables 8 and 9 , the enhanced xml schema according to the present invention defines a “ name ” attribute that is the list name of the & lt ; list & gt ; element , which was defined in the conventional schema in table 1 , as a child element of the & lt ; list & gt ; element , and additionally defines a new attribute “ id ” of a string type in the & lt ; list & gt ; element . this “ id ” attribute contains a random value that the system automatically allocates to the & lt ; list & gt ; element upon creating the & lt ; list & gt ; element . this “ id ” attribute should be unique among other & lt ; list & gt ; elements belonging to the same parent element in the shared uri list , and should remain unchanged before the & lt ; list & gt ; element vanishes . that is , this “ id ” attribute allows the & lt ; list & gt ; element to be uniquely identified in the resource - list document . in the present invention , this “ id ” attribute is used as a reference handle of the & lt ; external & gt ; element and the & lt ; resource - list & gt ; element used to refer to the & lt ; list & gt ; element . as described above , when the reference handle is used , only the & lt ; name & gt ; child element of the & lt ; list & gt ; element is changed and the “ id ” attribute that is used as a reference handle of the & lt ; list & gt ; element is kept unchanged even though the user changes the list name of the shared uri list later . accordingly , objects referring to the & lt ; list & gt ; element by using the “ id ” attribute as reference handle do not require the reference to be additionally updated according to the change in the list name of the shared uri list . further , a “ uri ” attribute indicating the uri value of the & lt ; entry & gt ; element , which was defined in the conventional xml schema of table 1 , is defined as the child element of the & lt ; entry & gt ; element in the enhanced xml schema of tables 8 and 9 , and a new attribute “ id ” of a string type is additionally defined in the & lt ; entry & gt ; element . this “ id ” attribute is a random value that is automatically allocated to the & lt ; entry & gt ; element of the system upon creation of the & lt ; entry & gt ; element , as in the above - described & lt ; list & gt ; element . the “ id ” attribute should be unique among other & lt ; entry & gt ; elements belonging to the same parent element in the shared uri list , and should remain unchanged until the & lt ; entry & gt ; element vanishes . as indicated above , the “ id ” attribute allows the & lt ; entry & gt ; element to be uniquely identified within the resource - list document , and is used as a reference handle of the & lt ; entry - ref & gt ; element , which is used to refer to the & lt ; entry & gt ; element . accordingly , only the & lt ; uri & gt ; child element of the & lt ; entry & gt ; element can be changed and the “ id ” attribute that is the reference handle of the & lt ; entry & gt ; element should remain unchanged , even if the user changes a uri of the shared member later . accordingly , objects referring to the & lt ; entry & gt ; element by using the “ id ” attribute as reference handle do not require the reference to be additionally updated according to the change in the uri of member in the shared uri list . table 10 shows enhancement of the conventional friends . xml resource - list document of table 2 , created according to the enhanced xml schema of the examples of tables 8 and 9 . table 10 shows an example according to the present invention in which lists and entries in the friends . xml document uses the randomly created “ id ” attribute values of sp93 , e21w , vn12w , and w2fb7 as reference handles . accordingly , friends . xml in table 10 , no longer uses the name or uri attribute values as reference handle , because they are subject to change at the discretion of the user owning friends . xml . as such , reference handles of friends . xml , which are introduced according to the present invention , do not change even when shared uri list service information is changed by the user . as described above , in the present invention , since the reference handle does not changes ( i . e ., it remains the same ), additional reference update of objects referring to the corresponding shared uri list according to the change in the reference handle is not required any more . accordingly , with the present invention , signaling overhead due to reference update is not required any more . in addition , system is simplified and its performance is improved since the reference update is not required . further , with the present invention , the conventional problem of interoperability degradation due to failure of reference update does not occur any more . further , according to the present invention , it is unnecessary to maintain information about the reference relationship of the shared uri list for possible reference update , and thus system resources are not wasted . tables 11 to 13 show examples of an improved resource - list document of a shared xdms , an improved rls - services document for rls service , and an improved poc group document for poc service , respectively , according to this invention . in tables 11 to 13 , all the reference relationships of those documents are improved by referring to the improved shared uri lists of friends . xml in table 10 , which is created according to the enhanced xml schema in table 9 . the examples of tables 11 to 13 show the enhanced versions of the “ name ” attribute , the “ uri ” attribute , and the reference handles in the examples shown in tables 5 to 7 . alternatively , the concept of reference handle used in the present invention can be achieved by improving the existing reference handles of ‘ name ’ attribute of & lt ; list & gt ; element and ‘ uri ’ attribute of & lt ; entry & gt ; element . however , as noted above , the respective value of ‘ name ’ attribute or ‘ uri ’ attribute shall be unique among those of other & lt ; list & gt ; element or & lt ; entry & gt ; element because this enables the unique identification of the corresponding & lt ; list & gt ; or & lt ; entry & gt ; element . as indicated above , the problems of the prior art are that these values are subject to change , and the existence of ‘ name ’ attribute is optional according to the schema definition in table 1 . therefore , if the value of ‘ name ’ attribute or ‘ uri ’ attribute is required to be static and the existence of ‘ name ’ attribute is mandatory , i . e ., a & lt ; list & gt ; element shall always contain the ‘ name ’ attribute , the static reference mechanism as presented by this invention can be achieved by modifying the existing reference handles . the signaling flow of creating and referring to a shared uri list according to the present invention is the same as illustrates in fig2 . that is , the created shared uri list is stored in the shared xmls , and xdm service information ( resource - list document ), rls service information ( rls service document ) and poc service information ( poc service document ) referring to the shared uri list are stored in the shared xdms , rls xdms , and poc xdms , respectively . service information stored in the shared xdms , rls xdms , and poc xdms are created by the enhanced xml schema according to the present invention . that is , the service information stored in the shared xdms , rls xdms , and poc xdms refers to the shared uri list using the randomly created reference handle . meanwhile , in the present invention , even when there is a change in the shared uri list , the reference handle is kept unchanged . accordingly , even when there is a change in a shared uri list , reference update of objects referring to the shared uri list is not required . fig4 is a flow diagram illustrating a signaling process for changing a shared uri list according to the present invention . as illustrated in fig4 , in the present invention , even when a shared uri list of the shared xdms 120 is changed by the user , i . e ., the xdm client 100 ( 401 and 403 ), reference updates for the other xdmss 120 , 130 , 140 , and 150 are not performed . in fig4 , an http 200 ok ( 405 or 407 ) is a response message . meanwhile , the process for creating the reference handle as described above is generally performed at the xdm client because the shared uri list is created at the xdm client and transmitted to the shared xdms . the process of creating the shared uri list at the xdm terminal according to the present invention will be described with reference to the accompanying drawings . fig5 is a flowchart illustrating a process of creating a shared uri list at an xdm client according to the present invention . as illustrated in fig5 , upon receipt of a request to create a shared uri list ( 500 ), the xdm client creates a reference handle in a corresponding shared uri list ( 502 ). generally , a random value is used as the reference handle . the xdm client creates the shared uri list including the created reference handle ( 504 ). the xdm client transmits the created shared uri list to the shared xdms ( 506 ). the xdm client creates service information referring to the created shared uri list and transmits it to each xdms for corresponding service ( 508 ). in the present invention , the reference handle value is , for the most part , meaningless to the user and is not notified to the user upon utilization of the shared uri list based on the reference for the oma service . accordingly , when the user requests a reference relationship , an operation for substantial reference is automatically performed and maintained by the system , i . e ., the xdm client , the shared xdms , the poc xdms , and the rls xdms . according to the present invention , oma services can stably refer to shared service information by creating a value that is not changed until the shared service information is deleted , and by using it as a reference handle in referring to the shared service information . therefore , signaling overhead , compatibility degradation , and resource waste can be prevented , and system performance can be improved . while the present invention has been shown and described with reference to exemplary embodiments thereof , it will be understood by those skilled in the art that various changes in from and detail may be made therein without departing from the scope of the present invention as defined by the following claims .