What are traditionally called possessive adjectives in English include my, your, our, his, her, and their. Its can be considered as part of this series or as an instance of the so-called genitive -s construction (normally spelled 's, but in this case it's is the abbreviation for it is). The genitive -s, like the possessive adjectives, can indicate possession, e.g.:
That's my hat.
That's your hat.
That's John's hat.That's the policewoman's hat.
Nouns with genitive -s can also function as nouns, corresponding to the forms traditionally called possessive pronouns, e.g.:
That hat is mine
That hat is yours
That hat is his
That hat is hers
That hat is ours
That hat is theirs
That hat is John's
That hat is the policewoman's
It is more accurate to refer to both possessive adjectives/pronouns and the -s genitive as realizations of genitive case, since possession is only one of many semantic relations which these constructions ma express. John's/his hat expresses possession (i.e. the hat that John/he possesses), but consider the following genitive expressions and their paraphrases:
the boy's/his application = the application which he made
my parents'/their consent = the consent which they-gave
the girl's/her story = the story she told
your telegram = the telegram you sent
the boy's/his release = the event or fact constituted by somebody releasing the boy
her promotion = the event or fact constituted by somebody promoting her
a women's college = a college for women (where only women study)
a summer's day = a day in summer (a summer day)
goat's milk = milk from goats (milk that goats produce)
There is a third type of genitive expression which is in many cases (but not always) equivalent to the -s genitive or possessive pronoun: this is the periphrastic or of genitive. For example:
the application of the boy
the consent of my parents
the story of the girl
the release of the boy
In what is called the double genitive this construction is combined with a possessive-pronoun or a noun with genitive -s, e.g.:
friend of mine
friend of yours
friend of John's
friend of the policewoman's
These expressions are equivalent to:
one of my friends
one of your friends
one of John's friends
one of the policewoman's friends
Although there is a great deal of overlap among these various types of genitive constructions, they are by no means always equivalent or interchangeable.