How to edit a file of edge attributes

[betty]

I am a new user of cytoscape. I edited a file of node attributes:
primarykey alias expressionstrength
a1 b1 0.3
a2 b2 0.4
a3 b3 0.5
The format is .xls.Then I imported the file sucessfully.But I came
across some problems when I tried to import a file of edge attributes:
primarykey alias interactionstrength
a1(pp)a2 e1 0.3
a2(pp)a3 e2 0.4
a3(pp)a1 e3 0.5
The format is .xls ,too.When I selected the file above in the user
interface,the status bar indicated that Keymatch:0.I don't know how to
deal with this question.
A detailed example and useful advice are wanted.

[betty]

I was so carless that I forgot to type a white space between the
sourece protein and the open parenthesis.After I corrected the error,I
imported the file successfully.