First at all, you must be sure that you have your database running and the appropriate jdbc database driver is in the classpath (or in the folder where the application has been unzipped). Below are some direct links to download the drivers for some databases (maven):

• Oracle Database JDBC Driver 6
• Microsoft JDBC Driver For SQL Server
• PostgreSQL JDBC Driver

The information required to access the database is explained below:

• Database connection info required for getConnection(): You must specify the driver class name and connection url along with the access credentials (if required). The driver class name and connection url is database vendor specific. Some examples of connections using the default ports are:

  Database Vendor	Class Driver Name	Connection url
  Oracle (OCI Driver)	oracle.jdbc.driver.OracleDriver	jdbc:oracle:oci:@<SERVER>:1521:ORCL
  SQL Server	com.microsoft.sqlserver.jdbc.SQLServerDriver	jdbc:sqlserver://<SERVER>:1433;database=<DATABASENAME>
  PostgreSQL	org.postgresql.Driver	jdbc:postgresql://<SERVER>:5432

  The option Connections in the menubar facitlitates the configuration for some typical connections.
  
• Database connection info required for getMetadata(): In order to obtain the database schema, the Java  getMetadata methods are used, which require additional information about the database catalog and database schema where to find the information about the database tables and views. This information is not allways required, but in many ocasions is needed, depending on the database vendor and the access privileges of the user who has access to the database. Below are some common scenarios: 
  • SQLServer: The catalog is the database name. and usually the schema is dbo. So as, in a common scenario you will specify the database name as catalog name and dbo as schema name. However, in many cases if you don't specify any information for schema or catalog you attain the same effect, provided that the user has only access to his database and dbo schema.
  • Oracle: The database username is asssociated with the schema and with a null catalog. So as, usually, you will not specify any catalog, but if you don't sypecify any schema, and click Load All Tables in Schema you will find all tables and views that this user has access to, possibly including system tables and tables from other schemas (if user has DBA privileges). Therefore, is highly recommended to specify the schema. 
  • PostgreSQL: The schema is usually public and with a null catalog.

The schema content is definde as indicated in the OpenApi specification (see DbSchema, DbTable and DbColumn in the Schemas section):

• The JSON representation is obtained by a Jackson serializer (empty or null attributes are omitted): An object representing the schema that contains an array of tables, each containing an array of columns. Attributes of the tables and columns contain the information related to name, data type, etc.
• The XML representation of the database schema consists on a root tag <schema> which contains a series of <table> tags. Each of them contains a <column> tag for each of the columns in this table. Attributes of the tags contain the information related to name, data type, etc

The schema may include three attributes, namely:

• dbms: Vendor's name of the database.
• catalog: Default catalog as specified in the connection info.
• schema: Default schema as specified in the connection info.

Both catalog and schema attributes are optional. However, they are relevent in order to determine what tables are to be found. Recall that according to the SQL Standard, a table specification may be qualified in the form [[catalog.]schema.]name. If a table name is not qualified (using catalog and/or schema), a default catalog and/or schema is assumed. In that case the deafaults are the indicated by dbcatalog and/or dbschema:

• If neither catalog nor schema are specified:
  • When loading all tables, all tables that are present in any schema are searched for. If the user has visibility over more than one catalog/schema and there are tables with the same name, an error occours because of a duplicated table name.
  • Given a set of tables, when you generate the schema, a similar error may occour if there are tables with same name that are visible. However, you may avoid this error by qualifying the table names that are duplicated. For instance, if a table T is present in two schemas S1 and S2, you will distinghish the tables by their qualified names S1.T and S2.T
• If catalog and/or schema are specified:
  • When loading all tables, all tables that match the catalog/schema specified are searched for. If some of dbcatalog or dbschema is not specified, it means any.
  • Given a set of tables, when the schema is generated, if a table name is not qualified, the table is searched for in the catalog/schema specified by default. If table name is qualified, the table is searched for in the catalog/schema as indicated by table name qualifier. For instance, if an schema S1 is specified by default, a table with name T will be searched in the schema S1, as same as if S1.T is specified. However, S2.T is specified, table T will be searched in the schema S2.

Latest builds of these applications has been tested with Java 1.8 on Windows and linux

As it uses standard jdbc methods to discover the database schema, it will work with virtually any database vendor, provided that you have the appropriate jdbc driver.