Consider a social network database, about people and their relationships. The database has two relations: Person(pid, name) Relationship(pid1, rel, pid2) Here Person. pid is a key, and Relationship. pid1 and Relationship. pid2 are foreign keys; rel is a string representing the relation type, and can be friend or enemy. Note that the relationship is not necessarily symmetric: if Alice is friend with Bob, this does not imply that Bob is friend with Alice. Write the SQL statements that define the relational schema for this database. Assume that pid's are integers, and name and rel are character strings.