boundry value analusis is a technique for test data 
selection.Test engineer chooses the values that lie along 
the data extreems.It includes max,mim,justinside,justout
side,typicalvalues and errorvalues.

Boundary Value Analysis is a technique used for writing the 
test cases..for example:If a particular field accepts the 
values from 1 to 1000, then we test that field by entering 
only 1, 1000, 0, 1001, 999,2.

i.e we check on the boundaries and then minimum-1 , minimum 
+1 and maximum+1, maximum-1.

Hai Nazeer,
    
    BVA is the most important in the testing in the block
box testing.

eg:
   
  IF u take yahoo user name suppose the client requirements is
  
 min 4 cha  and maxi 10 cha  in this place we apply the BVA is
          n-1  n  n+1                        m-1 m m+1
           ----|---------------------------------|----
           3   4  5                          9  10  11
hear the lower boundary value is 4 and upper boundary is 10
here we check  4-1,4,4+1,  and  10-1,10,10+1
Here 4-1,10+1 both are fail and 4,4+1,10-1,10 is pass

Thank you
saravanan.rk.qa@gmail.com