In macros two dots (..) are used to call a library if it is 
declared as a macro.

IF YOUR USING A SINGLE DOT i.e SCOTT.EMP YOU WONT GET ANY 
OUTPUT AND THE ERROR OCCURED IS WORK.SCOTTEMP DOES NOT EXIST

SO WE SHOULD USE TWO DOTS WHEN CALLING A LIB NAME AS A MACRO

%LET A=SCOTT /*LIBRARY NAME*/

PROC PRINT DATA=&A..EMP;
RUN;

to the above answer i add little .. is used for libref and 
one . for compiler and another for macro variable.

data new ;
input date ddmmyy10. ;
cards;
01/05/1955
01/09/1970
01/12/1975
19/10/1979
25/10/1982
10/10/1988
27/12/1991
;
run;

proc format ;
 
        value dat  low-'01jan1975'd=ddmmyy10.
             '01jan1975'd-'01JAN1985'd="Disco Years"
                      '01JAN1985'd-high=date9.;
   run;
 
proc print;
run;

proc print;
format date dat. ;
run;

DATA D1;
INPUT SLNO DATE DATE9. ;
DATALINES;
1 12DEC08
2 22NOV08
3 01JAN08
4 12FEB07
5 13MAR07
6 24APR06
7 17MAY06
8 20JUN05
9 29JUL05
10 30APR09
;
RUN;

proc format ;
 value KAVI  low-'31DEC2006'd='***ddmonyy***'
             '01JAN2007'd-'31DEC2007'd='***dd mon ccyy***'
             '01JAN2008'd-high='  **Disco Years **';
   RUN;
 
proc print data=D2 noobs label;
format DATE KAVI.;
RUN;