netweaver - Map complex data access business logic with oData -

i have table in db , want show/edit data odata. don't want expose rows entityset because business logic add information each field of each row:

example. have in db table 3 rows:

k   c1   c2   c3   c4 ---------------------- 01     b    d    e 02  f    g    h    03  l    m    n    o 04  p    q    r    s 

usera can:

• full control(create-read-update-delete) on each field (not modify-edit key can delete rows)

userb can:

• edit 2nd row

userc can:

• edit m, n , r

how can send complexity using odata?

1. how can recognize user logged ? (a sessionid string in header of http odata entityset?)
2. in metadata can expose different type of interaction data?
3. if want specify precise crud information (userb) how can pass informaions? (using complex type?)

these questions. odata, particularly full-descriptive concept of metadata, seems not marry complexity of data access.