B Advanced Topics in Oracle Label Security

Oracle provides advanced functionality for Oracle Label Security, such as the ability to analyze relationships between labels.

Topics:

Analyzing the Relationships Between Labels

You can analyze the relationships between labels.

Topics:

About Dominant and Dominated Labels

The relationship between two labels can be described in terms of dominance.

A user's ability to access an object depends on whether the user's label dominates the label of the object. If a user's label does not dominate the object's label, then the user is not allowed to access the object.

Label dominance is analyzed in terms of all its components: levels, compartments, and groups.

Table B-1 Dominance in the Comparison of Labels

Factor Criteria for Dominance

Level

For label1 to dominate label2, the level of label1 must be greater than or equal to that of label2.

Compartment

For label1 to dominate label2, the compartments of label1 must contain all the compartments of label2.

Group

For label1 to dominate label2, label1 must contain at least one of the groups of label2.

One label dominates another label if all of its components dominate the components of the other label. For example, the label HIGHLY_SENSITIVE:FINANCE,OPERATIONS dominates the label HIGHLY_SENSITIVE:FINANCE. Similarly, the label HIGHLY_SENSITIVE::WR_AP dominates the label HIGHLY_SENSITIVE::WR_AP, WR_AR.

Non-Comparable Labels

It is important to understand how labels can be compared with regard to dominance.

The relationship between two labels cannot always be defined by dominance. Two labels are non-comparable if neither label dominates the other.

If any compartments differ between the two labels (as with HS:A and HS:B), then they are non-comparable. Similarly, the labels HS:A and S:B are non-comparable.

You can find existing labels by querying the DBA_SA_LABELS data dictionary view.

Using Dominance Functions

Oracle Label Security provides functions to control dominance.

Topics:

About the Dominance Functions

You can use dominance functions to specify ranges in queries.

The following functions enable you to indicate dominance relationships between specified labels.

Table B-2 Functions to Determine Dominance

Function Description

OLS_DOMINATES

The value of label1 dominates, or is equal to, that of label2.

OLS_LABEL_DOMINATES

The value of the session label for the corresponding policy_name dominates, or is equal to, that of label.

OLS_STRICTLY_DOMINATES

The value of label1 dominates that of label2, and is not equal to it.

OLS_DOMINATED_BY

The value of label1 is dominated by that of label2.

OLS_STRICTLY_DOMINATED_BY

The value of label1 is dominated by that of label2, and is not equal to it.

Note that there are two types of dominance function. While the SA_UTL dominance functions return BOOLEAN values, the standalone dominance functions return integers.

OLS_DOMINATES Standalone Function

The OLS_DOMINATES (OLS_DOM) function returns 1 (TRUE) if label1 dominates label2, or 0 (FALSE) if it does not.

Syntax

OLS_DOMINATES (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN INTEGER; 

Parameters

Table B-3 OLS_DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SELECT OLS_DOMINATES ('1111', '1112') FROM DUAL;

OLS_DOMINATES('1111','1112')
----------------------------
                           0

Note:

The old OLS functions, DOMINATES and DOM, have been deprecated in Oracle Database 12c release 1 (12.1).

You can still use the old functions in this release, but Oracle recommends that you use the OLS_LABEL_DOMINATES and OLS_DOM functions instead. Using the new function names avoids potential name conflicts with other database components.

OLS_LABEL_DOMINATES Standalone Function

The standalone OLS_LABEL_DOMINATES function checks the dominance of session labels.

It returns 1 (TRUE) if the session label of the specified policy_name value dominates or is equal to the label that is specified by the label parameter. Otherwise, this function returns 0 (FALSE). This function is publicly available.

Note:

This feature is available starting with Oracle Database 12c release 1 (12.1.0.2).

In addition to Oracle Label Security policies, you can use this function with both Oracle Data Redaction and Oracle Database Vault policies.

Syntax

OLS_LABEL_DOMINATES (
  policy_name    IN VARCHAR2,
  label          IN VARCHAR2)
RETURN INTEGER;

Parameters

Table B-4 OLS_LABEL_DOMINATES Parameters

Parameter Description

policy_name

The name of the Oracle Label Security policy whose session label must be checked for dominance. To find existing label values for policies, query the POLICY_NAME and LABEL columns of the ALL_SA_LABELS view.

label

The base label against whom the dominance has to be checked

Examples

The following example checks if the session label for the hr_ols_pol policy dominates or is equal to the hs label.

SELECT OLS_LABEL_DOMINATES ('hr_ols_pol', 'hs') FROM DUAL;

OLS_LABEL_DOMINATES('HR_OLS_POL','HS')
--------------------------------------
                                     0

This example shows how you can use the OLS_LABEL_DOMINATES function in an Oracle Data Redaction policy:

BEGIN
 DBMS_REDACT.ADD_POLICY(
   object_schema   => 'oe', 
   object_name     => 'customers', 
   column_name     => 'customer_id',
   policy_name     => 'redact_cust_user_ids', 
   function_type   => DBMS_REDACT.FULL,
   expression      => 'OLS_LABEL_DOMINATES(''hr_ols_pol'', ''hs'') = 0');
END;
/

The following example shows how you can use the OLS_LABEL_DOMINATES function in an Oracle Database Vault rule definition:

EXEC DBMS_MACADM.CREATE_RULE('Check OLS Factor', 'OLS_LABEL_DOMINATES(''hr_ols_pol'', ''hs'') = 1');

See Also:

OLS_STRICTLY_DOMINATES Standalone Function

The OLS_STRICTLY_DOMINATES (OLS_S_DOM) function returns 1 (TRUE) if label1 dominates label2 and is not equal to it.

Syntax

OLS_STRICTLY_DOMINATES (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN INTEGER; 

Parameters

Table B-5 OLS_STRICTLY_DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Examples

The following example compares existing label tags 1111 and 1112.

SELECT OLS_STRICTLY_DOMINATES ('1111', '1112') FROM DUAL;

OLS_STRICTLY_DOMINATES('1111','1112')
-------------------------------------
                                    0

Note:

The old OLS functions, STRICTLY_DOMINATES and S_DOM have been deprecated in Oracle Database 12c release 1 (12.1).

You can still use the old functions in this release, but Oracle recommends that you use the OLS_STRICTLY_DOMINATES and OLS_S_DOM functions instead. Using the new function names avoids potential name conflicts with other database components.

OLS_DOMINATED_BY Standalone Function

The OLS_DOMINATED_BY (OLS_DOM_BY) function returns 1 (TRUE) if label1 is dominated by label2.

Syntax

OLS_DOMINATED_BY (
  label1          IN NUMBER,
  label2          IN NUMBER)
RETURN INTEGER;

Parameters

Table B-6 OLS_STRICTLY_DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SELECT OLS_DOMINATED_BY ('1111', '1112') FROM DUAL;

OLS_DOMINATED_BY('1111','1112')
-------------------------------
                              1

Note:

The old OLS functions, DOMINATED_BY and DOM_BY have been deprecated in Oracle Database 12c release 1 (12.1).

You can still use the old functions in this release, but Oracle recommends that you use the OLS_DOMINATED_BY and OLS_DOM_BY functions instead. Using the new function names avoids potential name conflicts with other database components.

OLS_STRICTLY_DOMINATED_BY Standalone Function

The OLS_STRICTLY_DOMINATED_BY (OLS_S_DOM_BY) function returns 1 (TRUE) if label1 is dominated by label2 and is not equal to it.

Syntax

OLS_STRICTLY_DOMINATED_BY (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN INTEGER; 

Parameters

Table B-7 OLS_DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SELECT OLS_STRICTLY_DOMINATES ('1111', '1112') FROM DUAL;

OLS_STRICTLY_DOMINATES('1111','1112')
-------------------------------------
                                    0

Note:

The old OLS functions, STRICTLY_DOMINATED_BY and S_DOM_BY have been deprecated in Oracle Database 12c release 1 (12.1).

You can still use the old functions in this release, but Oracle recommends that you use the OLS_STRICTLY_DOMINATED_BY and OLS_S_DOM_BY functions instead. Using the new function names avoids potential name conflicts with other database components.

SA_UTL.DOMINATES

The SA_UTL.DOMINATES function returns TRUE if label1 dominates label2 or if the session label for the given OLS policy dominates label.

Syntax

SA_UTL.DOMINATES (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN BOOLEAN; 

Syntax

SA_UTL.DOMINATES (
  ols_policy_name  IN VARCHAR2,
  label            IN VARCHAR2) 
RETURN BOOLEAN; 

Parameters

Table B-8 SA_UTL.DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SET SERVEROUTPUT ON
BEGIN 
 IF SA_UTL.DOMINATES(1111, 1112)
  THEN DBMS_OUTPUT.PUT_LINE('Label 1111 dominates label 1112.');
 ELSE 
  DBMS_OUTPUT.PUT_LINE('Label 1112 dominates label 1111.'); 
 END IF; 
END;
/

Label 1112 dominates label 1111.

Note:

The second SA_UTL.DOMINATES function, which takes the Oracle Label Security policy name and label as inputs, has been deprecated in Oracle Database 12c release 1 (12.1).

You can still use this function, but not with Oracle Data Redaction and Oracle Database Vault conditions. Oracle recommends that you use the OLS_LABEL_DOMINATES function instead.

The first SA_UTL.DOMINATES function, which uses the NUMBER datatype, is not deprecated.

SA_UTL.STRICTLY_DOMINATES

The SA_UTL.STRICTLY_DOMINATES function returns TRUE if label1 dominates label2 and is not equal to it.

Syntax

SA_UTL.STRICTLY_DOMINATES (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN BOOLEAN; 

Parameters

Table B-9 SA_UTL.STRICTLY_DOMINATES Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SET SERVEROUTPUT ON
BEGIN 
 IF SA_UTL.STRICTLY_DOMINATES(1111, 1112)
  THEN DBMS_OUTPUT.PUT_LINE('Label 1111 strictly dominates label 1112.');
 ELSE 
  DBMS_OUTPUT.PUT_LINE('Label 1112 strictly dominates label 1111.'); 
 END IF; 
END;
/

Label 1112 strictly dominates label 1111.

SA_UTL.DOMINATED_BY

The SA_UTL.DOMINATED_BY function returns TRUE if label1 is dominated by label2.

Syntax

SA_UTL.DOMINATED_BY (
  label1          IN NUMBER,
  label2          IN NUMBER) 
RETURN BOOLEAN;

Parameters

Table B-10 SA_UTL.DOMINATED_BY Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SET SERVEROUTPUT ON
BEGIN 
 IF SA_UTL.DOMINATED_BY(1111, 1112)
  THEN DBMS_OUTPUT.PUT_LINE('Label 1111 is dominated by label 1112.');
 ELSE 
  DBMS_OUTPUT.PUT_LINE('Label 1112 is dominated by label 1111.'); 
 END IF; 
END;
/

Label 1111 is dominated by label 1112.

SA_UTL.STRICTLY_DOMINATED_BY

The SA_UTL.STRICTLY_DOMINATED_BY function returns TRUE if label1 is dominated by label2 and is not equal to it.

Syntax

SA_UTL.STRICTLY_DOMINATED_BY (
  label1          IN NUMBER,
  label2          IN NUMBER)
RETURN BOOLEAN;

Parameters

Table B-11 SA_UTL.STRICTLY_DOMINATED_BY Parameters

Parameter Description

label1

The first label to check. To find existing label values, query the LABEL and TAG columns of the ALL_SA_LABELS view.

label2

The second label to check

Example

The following example compares existing label tags 1111 and 1112.

SET SERVEROUTPUT ON
BEGIN 
 IF SA_UTL.STRICTLY_DOMINATED_BY(1111, 1112)
  THEN DBMS_OUTPUT.PUT_LINE('Label 1111 is strictly dominated by label 1112.');
 ELSE 
  DBMS_OUTPUT.PUT_LINE('Label 1112 is strictly dominated by label 1111.'); 
 END IF; 
END;
/

Label 1111 is strictly dominated by label 1112.

Queries for Audited Oracle Label Security Session Labels

You can use the unified audit trail to capture information from various audit sources, including Oracle Label Security.

Topics:

About Queries for Auditing Oracle Label Security Session Labels

You must configure OLS auditing by creating unified audit policies.

OLS auditing enables you to audit additional events such as enabling and disabling of OLS policies.

The session labels that the audit trail captures are stored in the APPLICATION_CONTEXTS column of the UNIFIED_AUDIT_TRAIL view. You can use the LBACSYS.ORA_GET_AUDITED_LABEL function to retrieve session labels that are stored in the APPLICATION_CONTEXTS column. This function accepts the UNIFIED_AUDIT_TRAIL.APPLICATION_CONTEXTS column value, and the Oracle Label Security policy name as arguments, and then returns the session label that is stored in the column for the specified policy.

See Oracle Database Security Guide for detailed information about configuring and using OLS auditing in a unified audit trail.

ORA_GET_AUDITED_LABEL Function

The ORA_GET_AUDITED_LABEL function returns the audited session label for the specified OLS policy and APPLICATION_CONTEXTS column value.

The AUDIT_VIEWER role has EXECUTE privilege on the ORA_GET_AUDITED_LABEL function.

Syntax

ORA_GET_AUDITED_LABEL (
  appctx_col_value   IN VARCHAR2,
  ols_policy_name    IN VARCHAR2)
RETURN VARCHAR2;

Parameters

Table B-12 ORA_GET_AUDITED_LABEL Parameters

Parameter Description

appctx_col_value

Value in the UNIFIED_AUDIT_TRAIL.APPLICATION_CONTEXTS column

policy_name

The label security policy name

Example

The following example returns the audited session label for the hr_ols_pol policy.

SELECT ORA_GET_AUDITED_LABEL ('cust_ctx', 'hr_ols_pol') FROM DUAL;

ORA_GET_AUDITED_LABEL('X','HR_OLS_POL')
---------------------------------------
                                     HS

Oracle Call Interface for Setting Session Labels

You can use an Oracle Call Interface (OCI) to set session labels.

Topics:

About Using the Oracle Call Interface to Set Session Labels

When you connect using Oracle Call Interface (OCI), you can use the SYS_CONTEXT variables to initialize the session label and the row label.

You can set the variables using the OCIAttrSet function to initialize externally initialized SYS_CONTEXT variables. These are available when Oracle Label Security is enabled.

Each policy has a SYS_CONTEXT named SA$policy_name_X. You can set these two variables, INITIAL_LABEL and INITIAL_ROW_LABEL.

When the new values are set to valid labels within the user's authorizations, they will be used instead of the default values stored for the user. This is the same mechanism used for remote connections.

Using the Oracle Call Interface to Set Session Labels

You can use the Oracle Call Interface to set the session labels.

  1. Call OCIAttrSet with OCI_ATTR_APPCTX_SIZE to initialize the context array size with the desired number of context attributes:
    OCIAttrSet(session, OCI_HTYPE_SESSION, 
                     (dvoid *)&size, (ub4)0, OCI_ATTR_APPCTX_SIZE, error_handle); 
     
    

    This defines additional attributes for OCIAttrSet.

    Note that the size is ub4 type.

  2. Call OCIAttrGet with OCI_ATTR_APPCTX_LIST to get a handle on the application context list descriptor for the session:
    OCIAttrGet(session, OCI_HTYPE_SESSION, 
                   (dvoid *)&ctxl_desc, (ub4)0, OCI_ATTR_APPCTX_LIST, error_handle);
    

    Note that ctxl_desc is (OCIParam *) type.

  3. Call OCIParamGet with the application context list descriptor to obtain an individual descriptor for the i-th application context:
    OCIParamGet(ctxl_desc, OCI_DTYPE_PARAM, error_handle,(dvoid **)&ctx_desc, i);  
    

    Note that ctx_desc is (OCIParam *) type.

  4. Call OCIAttrSet with each of the three new attributes, OCI_ATTR_APPCTX_NAME, OCI_ATTR_APPCTX_ATTR, and OCI_ATTR_APPCTX_VALUE, to set the proper values in the application context:
    OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
                     (dvoid *)ctx_name, sizeof(ctx_name), OCI_ATTR_APPCTX_NAME,
                     error_handle);  
    
    OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
                     (dvoid *)attr_name, sizeof(attr_name), OCI_ATTR_APPCTX_ATTR,
                     error_handle);  
    
    OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
                     (dvoid *)value, sizeof(value), OCI_ATTR_APPCTX_VALUE,
                     error_handle);  
    

    Note that only character type is supported, because application context operations are based on the VARCHAR2 type.

Example: Using Oracle Call Interface with the SYS_CONTEXT Function

You can create an OCI call that uses an externalized SYS_CONTEXT function with Oracle Label Security.

Example B-1 shows how to accomplish this.

Example B-1 Using OCI to Externalize SYS_CONTEXT with OLS

#ifdef RCSID
static char *RCSid =
   "$Header: ext_mls.c 09-may-00.10:07:08 jdoe Exp $ ";
#endif /* RCSID */

/* Copyright (c) Oracle Corporation 1999, 2000. All Rights Reserved. */

/*

   NAME
ext_mls.c - externalized SYS_CONTEXT with Label Security

   DESCRIPTION
Run olsdemo.sql script before executing this example.
Usage: <executable obtained with .c file> <user_name> <password> <session-initial-label
Example: avg_sal sa_demo sa_demo L3:M,E:D10

   PUBLIC FUNCTION(S)
<list of external functions declared/defined - with one-line descriptions>

   PRIVATE FUNCTION(S)
<list of static functions defined in .c file - with one-line descriptions>

   RETURNS
The average salary in the EMP table of the SA_DEMO schema querying as the specified user with the specified session label.

   NOTES
<other useful comments, qualifications, and so on>

   MODIFIED   (MM/DD/YY)
jlev      09/18/03 - cleanup
jdoe      05/09/00 - cleanup
   jdoe      10/13/99 - standalone OCI program to test MLS SYS_CONTEXT
   jdoe      10/13/99 - Creation

*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>

static OCIEnv *envhp;
static OCIError *errhp;

int main(/*_ int argc, char *argv[] _*/);

/* get and print error */
static void checkerr(/*_OCIError *errhp, sword status _*/);
/* print error */
static void printerr(char *call);
static sword status;

/* return the average of employees' salary */
static CONST text *const selectstmt = (text *)
     "select avg(sal) from sa_demo.emp";
 
int main(argc, argv)
int argc;
char *argv[];
{
  OCISession *authp = (OCISession *) 0;
  OCIServer *srvhp;
  OCISvcCtx *svchp;
  OCIDefine *defnp = (OCIDefine *) 0;
  dvoid *parmdp;
  ub4 ctxsize;
  OCIParam *ctxldesc;
  OCIParam *ctxedesc;
  OCIStmt *stmtp = (OCIStmt *) 0;
  ub4 avg_sal = 0;
  sword status;

  if (OCIInitialize((ub4) OCI_DEFAULT, (dvoid *) 0,
                    (dvoid * (*)(dvoid *, size_t)) 0,
                    (dvoid * (*)(dvoid *, dvoid *, size_t)) 0,
                    (void (*)(dvoid *, dvoid *)) 0))
    printerr("OCIInitialize");

  if (OCIEnvInit((OCIEnv **) &envhp, OCI_DEFAULT, (size_t) 0, (dvoid **) 0))
    printerr("OCIEnvInit");
  
  if (OCIHandleAlloc((dvoid *) envhp, (dvoid **) &errhp, OCI_HTYPE_ERROR,
                     (size_t) 0, (dvoid **) 0))
    printerr("OCIHandleAlloc:OCI_HTYPE_ERROR");

  if (OCIHandleAlloc((dvoid *) envhp, (dvoid **) &srvhp, OCI_HTYPE_SERVER,
                     (size_t) 0, (dvoid **) 0))
    printerr("OCIHandleAlloc:OCI_HTYPE_SERVER");

  if (OCIHandleAlloc((dvoid *) envhp, (dvoid **) &svchp, OCI_HTYPE_SVCCTX,
                     (size_t) 0, (dvoid **) 0))
    printerr("OCIHandleAlloc:OCI_HTYPE_SVCCTX");

  if (OCIServerAttach(srvhp, errhp, (text *) "", strlen(""), 0))
    printerr("OCIServerAttach");

  /* set attribute server context in the service context */
  if (OCIAttrSet((dvoid *) svchp, OCI_HTYPE_SVCCTX, (dvoid *) srvhp,
                 (ub4) 0, OCI_ATTR_SERVER, (OCIError *) errhp))
    printerr("OCIAttrSet:OCI_HTYPE_SVCCTX");

  if (OCIHandleAlloc((dvoid *) envhp, (dvoid **) &authp,
                     (ub4) OCI_HTYPE_SESSION, (size_t) 0, (dvoid **) 0))
    printerr("OCIHandleAlloc:OCI_HTYPE_SESSION");

  /* set application context to 1 */
  ctxsize = 1;

  /* set up app ctx buffer */
  if (OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) &ctxsize,
                 (ub4) 0, (ub4) OCI_ATTR_APPCTX_SIZE, errhp))
    printerr("OCIAttrSet:OCI_ATTR_APPCTX_SIZE");

  /* retrieve the list descriptor */
  if (OCIAttrGet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION,
                 (dvoid *) &ctxldesc, 0, OCI_ATTR_APPCTX_LIST, errhp))
    printerr("OCIAttrGet:OCI_ATTR_APPCTX_LIST");

  if (status = OCIParamGet(ctxldesc, OCI_DTYPE_PARAM, errhp,
                           (dvoid **) &ctxedesc, 1))
    {
      if (status == OCI_NO_DATA)
        {
          printf("No Data found!\n");
          exit(1);
        }
    }

  /* set context namespace to SA$<pol_name>_X */
  if (OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "SA$HUMAN_RESOURCES_X",
                 (ub4) strlen((char *) "SA$HUMAN_RESOURCES_X"),
                 (ub4) OCI_ATTR_APPCTX_NAME, errhp))
    printerr("OCIAttrSet:OCI_ATTR_APPCTX_NAME:SA$HUMAN_RESOURCES_X");

  /* set context attribute to INITIAL_LABEL */
  if (OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "INITIAL_LABEL",
                 (ub4) strlen((char *) "INITIAL_LABEL"),
                 (ub4) OCI_ATTR_APPCTX_ATTR, errhp))
    printerr("OCIAttrSet:OCI_DTYPE_PARAM:INITIAL_LABEL");

  /* set context value to argv[3] - initial label */
  if (OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) argv[3],
                 (ub4) strlen((char *) argv[3]),
                 (ub4) OCI_ATTR_APPCTX_VALUE, errhp))
    printerr("OCIAttrSet:argv[3]");

  /* username first command line argument */
  if (OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) argv[1],
                 (ub4) strlen((char *) argv[1]), (ub4) OCI_ATTR_USERNAME,
                 errhp))
    printerr("OCIAttrSet:username");

  /* password second command line argument */
  if (OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION, (dvoid *) argv[2],
                 (ub4) strlen((char *) argv[2]), (ub4) OCI_ATTR_PASSWORD,
                 errhp))
    printerr("OCIAttrSet:password");

  if (OCISessionBegin(svchp, errhp, authp, OCI_CRED_RDBMS, (ub4) OCI_DEFAULT))
    printerr("OCISessionBegin");

  if (OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *) authp,
                 (ub4) 0, (ub4) OCI_ATTR_SESSION, errhp))
    printerr("OCIAttrSet:OCI_ATTR_SESSION");

  if (OCIHandleAlloc((dvoid *) envhp, (dvoid **) &stmtp, OCI_HTYPE_STMT,
                     0, 0))
    printerr("OCIHandleAlloc:OCI_HTYPE_STMT");

  if (OCIStmtPrepare(stmtp, errhp, (CONST OraText *) selectstmt,
                     (ub4) strlen((const char *) selectstmt),
                     (ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT))
    printerr("OCIStmtPrepare");

  if (OCIDefineByPos(stmtp, &defnp, errhp, (ub4) 1, (dvoid *) &avg_sal,
                     (sb4) sizeof(avg_sal), SQLT_INT, 0, 0, 0, OCI_DEFAULT))
    printerr("OCIDefineByPos");

  if (status = OCIStmtExecute(svchp, stmtp, errhp, 1, 0, NULL, NULL,
                              OCI_DEFAULT))
    {
      if (status == OCI_NO_DATA)
        {
          printf("No Data found!\n");
          exit(1);
        }
    }

  if (OCISessionEnd(svchp, errhp, authp, OCI_DEFAULT))
    printerr("OCISessionEnd");

  printf("average salary is: %d\n", avg_sal);
}

void checkerr(errhp, status)
     OCIError *errhp;
     sword status;
{
  text errbuf[512];
  sb4 errcode = 0;

  switch (status)
    {
    case OCI_ERROR:
      (void) OCIErrorGet((dvoid *) errhp, 1, NULL, &errcode, errbuf,
                         (ub4) sizeof(errbuf), OCI_HTYPE_ERROR);
      printf("Error - %.*s\n", 512, errbuf);
      break;
    default:
      break;
    }
}

void printerr(call)
     char *call;
{
  printf("Error: %s\n", call);
}
/* end of file ext_mls.c */