About Variable:
1.Variable 是和InfoObject绑定的，可用于任何含有该IO的query中。
2.Variable有以下几种类型：
Characteristic：用于限制Char。 
Text：用于在报表动态显示文本。 
Hierarchy：用于限制Hierarchy。 
Hieararchy Node：用于限制Hierarchy Node。 
Formula: 可以在公式中使用变量，让用户输入一个数，读取某个Char.的属性（例如Prduct的price属性)等来用于计算。 
Offset的应用：设置偏移量
SAP BI Content内置了很多标准变量。当其无法满足需求时，有时仅仅需要设置下偏移量就可以满足需求了。
例如系统已经有了当前月份的变量，通过偏移就可以获得上N个月和下N个月的变量，无需增强。
 
定义Customer Exit Variables（BW 3.x ，BI7 类似）
客户出口变量可以通过程序来处理变量逻辑。定义过程如下：
1.在query designer中，右键单击要建立变量的characteristic,选择New variable.
2.设置为customer exit类型
3.进入CMOD，修改：Enhancement   Exp  RSR00001 BI: Enhancements for Global Variables in Reporting-->Function exit    EXIT_SAPLRRS0_001-->INCLUDE ZXRSRU01 。该Function Module 将在query运行时被调用多次。
3-1：调用前，系统将其他变量的当前值保存在内表 I_T_VAR_RANGE中。The table type is RRS0_T_VAR_RANGE, and row type RRS0_S_VAR_RANGE references structure RRRANGEEXIT.This structure has the following fields: 
Field                                     Description
 
VNAM                                   Variable name
 
IOBJNM                                 InfoObject name
 
SIGN                                      (I)ncluding [ ] or (E)xcluding ] [
 
OPT                                      Operators: EQ =, BT [ ], LE <=, LT <, GE >=, GT >, CP, and so on
 
LOW                                      Characteristic value
 
HIGH                                      Characteristic value of upper limit for intervals or node InfoObject for hierarchy nodes
 3-2：每次调用时，系统会传递参数值给Function Module。其中，比较重要的参数如下：

I_STEP 标识了该调用发生的时机：

I_STEP = 1: Call is made directly before variable entry.
I_STEP = 2: Call is made directly after variable entry. This step is only executed if the same variable is not input-ready and could not be filled for I_STEP = 1.
I_STEP = 3: In this call, you can check the values of the variables. When an exception (RAISE) is triggered, the variable screen appears again. I_STEP = 2 is then also called again.
 I_STEP = 0: The enhancement is not called from the variable screen. The call can originate from the authorization check or from the monitor.
I_VNAM标识了当前要处理的变量。

3-3：完成变量的处理之后，应将变量的值写入E_T_RANGE。

Sample Code:
DATA: L_S_RANGE TYPE RSR_S_RANGESID.
DATA: L_S_VAR_RANGE TYPE RRRANGEEXIT. 
CASE I_VNAM.  
     WHEN 'CUMMONTH'.
        IF I_STEP = 2. "after the popup 
            READ TABLE I_T_VAR_RANGE INTO L_S_VAR_RANGE WITH KEY VNAM = 'MONTH'.
            IF SY-SUBRC = 0.
                    CLEAR L_S_RANGE.
                    L_S_RANGE-LOW = LOC_VAR_RANGE-LOW(4)."low value, for example, 200601
                    L_S_RANGE-LOW+4(2) = '01'.
                    L_S_RANGE-HIGH = LOC_VAR_RANGE-LOW. "high value = input
                    L_S_RANGE-SIGN = 'I'.
                    L_S_RANGE-OPT = 'BT'.
                   APPEND L_S_RANGE TO E_T_RANGE.
                ENDIF.
        ENDIF.
ENDCASE.

查看SAP Exit变量 
SAP Exit变量为我们编写customer exit变量提供了很好的参考。
1. SE16 查看表 RSZGLOBV 可以得到系统全部变量的列表，选择process type=SAP Exit，即可获得所有的SAP Exit变量列表
2. SE37 查看 RREX_VARIABLE_EXIT 或RSVAREXIT_ * 可以找到SAP Exit变量的代码