Writing the interface definatinon inside the libaray in .idl file

[C++ Programming]

hi
what is the diffrence, if i write the interface declaration inside library in my .idl file . Are these two implementation serve the same purpose.

for Ex:

library XYZ
{
interface ABC
{
method 1 ;
}
[
uuid(________),
helpstring("_________")
]

coclass PQR
{
[default]interface ABC;
};
};

OR

interface ABC
{
method 1 ;
};

library XYZ
{
[
uuid(________),
helpstring("_________")
]

coclass PQR
{
[default] interface ABC ;
};
} ;