Create README.md

Author: MichaelDaum

README.md

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+# DBIPlugin
+Database middle layer to manage connections and schemes
+
+This plugin offers a middle layer for Foswiki extensions to ease connecting to 
+SQL databases and manage schemes of table and index definitions. The idea is to
+keep things as lean as possible without imposing any additional structure. <nop>DBIPlugin
+will maintain a plugin's database scheme to make sure it is created and updated as required.
+
+A plugin sub-classes Foswiki::DBI::Schema which is then loaded before
+connecting to a database. While connecting to the database the schema then is added to the database.
+
+<nop>DBIPlugin supports any database for which a DBD perl driver is available. A plugin may support
+multiple databases where the schemes differ in parts. For example the schema for SQLite differs
+from the one for <nop>MariaDB, <nop>MySQL or <nop>PostgreSQL. The plugin will then implement:
+
+   * Foswiki::DBISchema::SQLite
+   * Foswiki::DBISchema::MariaDB
+   * Foswiki::DBISchema::MySQL
+   * Foswiki::DBISchema::PostgreSQL
+
+The syntax of each of them are custom tailored towards the respective database vendor. Note
+however that from there on it is the plugin's responsibility to cope with further differences
+among databases beyond just schema definitions.
+
+Have a look at DBIPluginPerlAPI for further information.