1.6.1 Realising the design
So far we have been concerned only with the specification of a logical schema. We now need our database to be created according to the definitions we have produced. For an implementation with a relational DBMS, this will involve the use of SQL to create tables and constraints that satisfy the logical schema description and the choice of appropriate storage schema (if the DBMS permits that level of control).
One way to achieve this is to write the appropriate SQL DDL statements into a file that can be executed by a DBMS so that there is an independent record, a text file, of the SQL statements defining the database. Another method is to work interactively using a database tool like Sybase Central (or Microsoft Access), where the forms provided for defining tables help avoid the need to remember the syntactic detail of the SQL language. While this may seem to make it easier to realise a database, it can lead to maintenance problems. In this case, there can be a problem keeping track of exactly how tables are defined and the ability to make changes to them, so it is not recommended for large development projects.
Whatever mechanism is used to implement the logical schema, the result is that a database, with tables and constraints, is defined but will contain no data for the user processes.