do you mean how are the two similar to each other...

some people with borderline personality disorder also have symptoms of altered personality states...ego states, introjects, fragmentation of states of mind that are noticeable (the adult, parent and child parts of self) and unstable moods swings that change frequently

some borderline people also have unstable relationships, difficulty making friends/keeping friends/ rocky intimate relationships.

some people with borderline personality disorder have low self image/low self esteme/low self worth...

some people with borderline personality disorder have episodes of psychosis (retreating into internalized worlds where they lose touch with reality, expect reality to be the same as their internal world/delusional thoughts/delusional behaviors/ hallucinations/ paranoia/...)

some people with borderline personality disorder have trouble with memories/ remembering things...

with DID....

the person has a special type of alternate personalities/altered states of mind.

some people with DID have introjects/ego states/adult, parent child type fragmentation besides having the DID type alters that fit the diagnostic criteria.

some people with DID have internal worlds

some people with DID have unstable mood swings.

some people with DID have low self esteem/low self worth/low self image...

some people with DID have unstable relationships with family friends and intimate partners. Some have trouble making and keeping friends.

some people with DID have trouble with episodes of psychosis (hallucinations, retreating into their internal worlds/delusional thought/delusional behaviors...)

people with DID have memory problems.