text: the following detailed description of the embodiments do not limit the implementation of the embodiments to any particular computer programming language . the computer program product may be implemented in any computer programming language provided that the operating system provides the facilities that support the requirements of the computer program product . a preferred embodiment is implemented in the c or c ++ computer programming language ( or may be implemented in other computer programming languages in conjunction with c / c ++). any limitations presented would be a result of a particular type of operating system , computer programming language , or data processing system and would not be a limitation of the embodiments described herein . fig1 illustrates a configuration of a computing environment 100 comprising a data processing system 126 in which an embodiment of a database management system 122 may be implemented . the data processing system 126 includes a central processing unit ( cpu ) 102 , a memory 104 , an input / output interface 106 and a bus 108 . the cpu 102 , the memory 104 and the input / output interface 106 are connected with one another via the bus 108 . the input / output interface 106 is configured so that it can be connected to an input / output unit 112 in the computing environment 100 . the cpu 102 can be a commercially available cpu or a customized cpu suitable for operations described herein . other variations of the cpu 102 can include a plurality of cpus interconnected to coordinate various operations and functions . the data processing system 126 serves as an apparatus for performing the present method by the cpu 102 executing the present invention . data and instructions that are to be executed by the cpu 102 reside in the memory 104 . the memory 104 contains a database management system ( dbms ) 122 and a database 110 with multiple tables 116 ( only one table is shown for illustration purposes ) that hold information . the instructions are internal representations of programs that run on the data processing system 126 , such as the database management system 122 . the programs operate on the data . for example , if the program is the database management system 122 , the data can be rows in the table 116 . the database management system 122 comprises a compiler 118 and an external system interface 124 . the database management system 122 retains an indication of operating conditions , such as an identifier for the user who submitted the query 114 , when compiling and executing the query 114 . the information in the tables 116 may be accessed by a query 114 that is received by the input / output unit 112 and is retained in the memory 104 . the query 114 may be presented in an sql format that is compiled by the compiler 118 to form an internal representation that is interpreted for execution . the present invention may be embodied in the compiler 118 . alternatively , the present invention may be provided as an extension of the functionality of the compiler 118 . the present invention may be embodied in a program stored in , for example , the memory 104 . alternatively , the present invention may be recorded on any type of recording medium such as a magnetic disk or an optical disk . the present invention recorded on such a recording medium is loaded to the memory 104 of the data processing system 126 via the input / output unit 112 ( e . g . a disk drive ). the compiler 118 recognizes statements in the query 114 including keywords that represent commands and relevant arguments . during the formation of the internal representation from the query 114 , the compiler 118 modifies the query 114 to improve performance during execution . the external system interface 124 is in communication with an external system 120 while modifying the query 114 to improve performance . the external system 120 may be a system external to the database management system 122 but residing in the data processing system 126 or it may be external to the data processing system 126 . in the latercase the external system 120 may communicate with the data processing system 126 via a direct link or through a communications network . the external system 120 manages the assignment of classifications to users and sections of data in the tables 116 . for example , given a user identification and a table name , the external system 120 knows how to obtain the classification of that user . the external system 120 contains a classification that is associated with the query 114 which may be a classification for a user identification from which the query 114 was submitted , a classification of the location from which the query 114 was submitted or some other such similar classification basis . the external system 120 may also contain access rules that govern when a user with a particular classification can access an element from the table 116 . an interface in the external system 120 accepts questions from the compiler 118 providing available information and desired information . through this interface the external system 120 is able to either provide the information requested by the compiler 118 or provide a course of action for obtaining the information . as a result , the query 114 may be modified to include information on a user &# 39 ; s classification or table classification or a comparison of the two classifications . such information might be determined by interfacing with the external system 120 during execution or such interfacing may be performed in advance by the compiler 118 and the results incorporated into the query 114 . fig2 illustrates operations of the compiler 118 that modify the query 114 based on information from the external system 120 . the query 114 , containing at least one request for information , is read in step 202 . each request is analyzed in step 204 to extract parameters of the request and a target of the request . the type of information of each of the parameters is determined in step 206 . the parameters may also include an identification associated with the query 114 such as a user who submitted the query 114 or a location of the submission . the type of information requested from the target is determined in step 208 . the table 116 in the database 110 contains information that is classified . in order for a user who submitted the query 114 to obtain the requested information from the table 116 , access rules for the table 116 in the external system 120 might indicate that the user have a classification that corresponds to the classification of the requested information . based on the types of parameters included in the request , the user &# 39 ; s identification ( as contained in the database management system 122 ) and the type of information requested , step 210 determines what information regarding the user &# 39 ; s classification and the information &# 39 ; s classification is unknown . since this unknown classification information is determined prior to completing execution of the query 114 , the compiler 118 determines how the classification information can be determined in conjunction with the external system 120 . a request for a strategy to obtain the unknown classification information is generated in step 212 . this request is based on the determined types of the parameters and the determined type of the requested information . suggested course ( s ) of action for obtaining the unknown classification information are received in step 214 from the external system 120 . if there are multiple types of unknown classification information then there may be multiple courses of action that will be received . each course of action received may be directed to obtaining one of the types of unknown classification information . if there is more than one course of action received , as determined in step 216 , then an order for the courses of action is determined in step 218 . this order may depend on information required by each course of action . for example , if one course of action uses information dependent on a second course of action then the second course of action is implemented first . the order for implementation of the courses of action may optionally be supplied with the suggested courses of action the course ( s ) of action are inserted into the query in step 220 such that they can be easily implemented during execution . fig3 illustrates functional components of the compiler 118 in the dbms 122 for modifying the query 114 based on information from the external system 120 . the external system 120 includes a request interface 300 and a request processing mechanism 302 . the compiler 118 includes a controller 304 in communication with a query analysis mechanism 306 , a management interface 308 , an information analysis mechanism 314 , a query classification mechanism 310 and a request formation mechanism 312 . the controller 304 in the compiler 118 manages compiling the query 114 in order to form an internal representation thereof . during compiling , the controller 304 coordinates modification of the query 114 to improve execution performance . when the controller 304 detects a request in the query 114 that requires a check of a user &# 39 ; s classification with the classification of requested information , the request is provided to the query analysis mechanism 306 . the query analysis mechanism 306 includes a target type mechanism 316 and a parameter type mechanism 318 that collectively function to determine the information defining the request and the information sought from the request . the parameter type mechanism 318 extracts the type of information of the parameters that define the request . the target type mechanism 316 determines the type of information that has been requested . the query analysis mechanism 306 provides the parameters and target types to the controller 304 where it is passed to the information analysis mechanism 314 and the request formation mechanism 312 . the information analysis mechanism 314 receives the parameters and target types and assesses what information is available for determining the requested information classification and user &# 39 ; s classification . based on the available information , the information analysis mechanism 314 determines the information that is unknown that is to be used for completing data access qualification for the user . the determined unknown information is provided to the controller 314 from which it is passed to the request formation mechanism 312 . the request formation mechanism 312 receives the parameters and target types as well as an indication of the unknown information to be used in determining the requested information classification and user &# 39 ; s classification . the request formation mechanism 312 formulates a request on how to obtain the unknown information based on the parameters and target types . this request is provided to the controller 304 to be passed to the management interface 308 . the external system interface 308 provides the request to the external system interface 124 in the database management system 122 so that the request can be submitted to the external system 120 . the request from the request formation mechanism 312 may be one or a combination of , for example : q1 : given an user identification and a table name , how can the user classification be obtained ? q2 : given a set of data values and a table name , how can the element classification be obtained ? q3 : given a user classification and an element classification , how can the two be compared ? the request interface 300 of the external system 120 receives the request from the compiler 118 . the request is provided to the request processing mechanism 302 where a knowledge base may be drawn upon to produce suggestions regarding the manner in which the unknown information can be obtained . if there are multiple courses of action then the suggestion may involve multiple courses of action , each pertaining to obtaining a different piece of unknown information . the suggestions from the request processing mechanism 302 are provided to the controller 304 via the request interface 300 and the management interface 308 through the external system interface 124 . based on the above exemplary requests , the suggested course ( s ) of action form the request processing mechanism 302 may be one or a combination of , for example : a1 : a subquery which can be used to select a user classification or element classification from a table in the database 110 known to the external system 120 . a2 : a predicate which can be used to filter out the table &# 39 ; s elements ( rows or columns ) that have a classification that do not match the user &# 39 ; s classification . a3 : a set of values presented directly or indirectly via a session variable or special register . these values can represent a set of user classification or a set or element classifications . a4 : a query which can be used to generate an internal mapping table for use by the executable form of the query 114 . for a given table , the mapping table enables identification of the classification of an element in the table . for example , the mapping table may consist of ( n + 1 ) columns where the first n columns represent the table columns from which to derive the element classifications and the last columns represents a classification level . when such a mapping table was not previously created , an internal mapping table for use by the executable form of the query 114 can be generated for this purpose . a5 : a request to call the external system at execution time of the query 114 for classification information . the above requests may produce the suggested course ( s ) of action as indicated below : action on q1 : a1 : a subquery that can be used to select the user classification for the user identification from a database table known to the external system 120 . a3 : a data value ( s ) that indicates the user classification for the user identification . a5 : an indication that the external system 120 should be asked for this information at execution time . action on q2 : a1 : a subquery that can be used to select the element classification for the current element from a mapping table known to the external system 120 . a4 : a query that can be used to generate an internal mapping table for use by the executable form of the query 114 . a5 : an indication that the external system 120 should be asked for this information at execution time . action on q3 : a2 : a predicate that the compiler 118 can add to the query 114 to filter out the table &# 39 ; s elements that do not match the user &# 39 ; s classification . the general form of predicates returned will be an in predicate but inequality predicates are also possible , particularly if the element classification or user &# 39 ; s classification represent a hierarchy . this type of advice is most likely to be returned when the element classification is stored within the table itself or when a mapping table has been created . if the element classification is stored within the element then the predicate will refer to the table &# 39 ; s column where the element classification level is stored , otherwise , the predicate will refer to the mapping table &# 39 ; s column where the classification level is stored . a3 : a set of values representing the element classification allowed for the given user &# 39 ; s classification . element level access control may then be enforced by , for example : 1 . the compiler 118 altering the query 114 to add a predicate using the set of values received . this choice is possible if the element classification is stored within the table itself or a mapping table has been created . 2 . if the element classification is not stored within the table and a mapping table has not been created then a predicate cannot be used . in this case , interaction between the dbms 122 and the external system 120 is used during execution of the query 114 to enforce element access control . for each element accessed , the data in the set of columns defining the element classification and the full table is submitted to the external system 120 with the result being the element classification . the result is compared against the set of values for the given user classification to determine if the element can be viewed or altered by that user . to reduce the number of times the dbms 122 makes a call to the external system 120 to obtain the element classification a caching technique may be used . for example , the information that could be stored in the cache may be the full table name , the data defining the element classification and the element classification as returned by the external system 120 . a5 : an indication that the external system 120 should be asked for this information at execution time . the request provided by the request processing mechanism 302 may also provide an indication of whether or not the suggested course ( s ) of action can be used of all users or only for a provided user identification . the controller 304 provides the suggested course ( s ) of action to the query classification mechanism 310 where an order is determined for the course ( s ) of action based on dependence of the results of each course of action . alternatively , this order may be specified by the external system 120 and received with the suggested course ( s ) of action . after the order has been determined , the query classification mechanism 310 modifies the query 114 to include the course ( s ) of action . the following are examples of modifying an sql query to include obtaining classification information . a table t1 ( c1 , c2 , c3 , . . . , cn ) represents a table where the classification level of an element and the user classification is an element of the ordered set s ={ top secret , secret , confidential , classified , unclassified }. the element level access control policy for this example states that an element with a classification r can be viewed by a user with a classification u only if u & gt ;= r . suppose that a user with a classification level ‘ confidential ’ issues a query select * from t1 . the compiler 118 sends a request corresponding with q1 from above to the external system 120 to obtain the user &# 39 ; s classification . suppose the external system 120 provides a suggested course of action corresponding with a3 from above ; that is , a data value representing the user &# 39 ; s classification . the compiler 118 then submits a second request to the external system 120 based on q3 above by submitting the table name ( t1 ) and the user &# 39 ; s classification ( confidential ). suppose the external system 120 returns a suggested course of action corresponding with a2 from above . that is , in response to the second request the external system 120 returned a predicate in , for example , “ c1 in (‘ confidential ’, ‘ classified ’, ‘ unclassified ’)”. based on the received courses of action the compiler 118 modifies the query 114 to incorporate the predicate providing a query such as given that the set is ordered and represents a hierarchy , the predicate returned could also be “ c1 & gt ;‘ confidential ’. suppose an element classification is determined based on the values in columns c1 and c2 as follows : c1 c2 element classification 1 1 top secret 2 2 secret 3 3 confidential 4 4 classified 5 5 unclassified the compiler 118 sends the external system 120 a request corresponding with request q1 to obtain the user &# 39 ; s classification . suppose the suggest course of action is a3 ; that is , a data value represent the user &# 39 ; s classification . the compiler 118 submits a second request based on the table name ( t1 ) and the set of column names defined in the classification mapping shown above ( cl and c2 ). the suggested course of action in response to the second request depends on whether a mapping table exists . a database table ( t1map ) storing mapping information has been created and is known to the external system 120 . t1map consists of three columns , namely , c1 , c2 and level . for each pair of values ( c1 , c2 ), the level column indicates an element classification . based on this information , the external system 120 can return a1 as the suggested course of action ; that is , a subquery to select an element classification from t1map . the subquery would be as follows : the compiler 118 then sends a request to the external system 120 corresponding with request q3 by submitting the table name ( t1 ) and the user &# 39 ; s classification ( confidential ). if the external system 120 returns suggested action a2 , then the predicate returned would be : “ t1map . level & gt ;‘ confidential ’”. based on the suggested course of action the compiler 118 modifies the query 114 to incorporate the predicate and subquery . the modified query would be : select * from t1 , t1map where ( t1 . c1 = t1map . c1 and t1 . c2 = t1map . c2 ) and ( t1map . level & gt ; ‘ confidential ’). if a mapping table does not exist then the suggested course of action provided to the compiler 118 might be action a5 , an indication to submit the same request during execution . the second request submitted by the compiler 118 corresponds with request q3 and submits the table name ( t1 ) and the user &# 39 ; s classification ( confidential ). the external system may provide action a3 , a set of data values representing the element classifications allowed for the user ( i . e . all elements having ‘ confidential ’, ‘ classified ’, and ‘ unclassified ’). based on the suggestion course of action the compiler 118 does not modify the query 114 but inserts logic into the internal representation to perform the following tasks : for each element obtained , call the external system 120 by submitting the table name ( t1 ) and the values ( c1 , c2 ). obtain the element classification from the call to the external system 120 . if the element classification is an element of the set {‘ confidential ’, ‘ classified ’, ‘ unclassified ’} then include the element in the result set ; otherwise , discard the element . although the classification of the user is used as the basis for obtaining the requested element of data , any classification associated with the query 114 may be used . such other associated classifications may include a classification of the location from which the query 114 was submitted . the elements of data that are accessed may be the rows of the tables 116 or the columns of the tables 116 or some other delineation of portions of the tables 116 . it will be appreciated that the elements described above may be adapted for specific conditions or functions . the concepts of the present invention can be further extended to a variety of other applications that are clearly within the scope of this invention . having thus described the present invention with respect to preferred embodiments as implemented , it will be apparent to those skilled in the art that many modifications and enhancements are possible to the present invention without departing from the basic concepts as described in the preferred embodiment of the present invention . therefore , what is intended to be protected by way of letters patent should be limited only by the scope of the following claims .