Meta object model for relational data storage: Difference between revisions

== Converting the Meta Model into a database structure ==

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This basic model can than be easily extended. For example in our case we want a sort order in links table. And because some databases are very slow at deleting rows, or just in case we may want a revision safe system there is an easy way to achieve that: Add a new table activity which basically has a timestamp. All the table on the instance layer get two additional columns: created_activity_id and deleted_activity_id. This is a lit bit redundant but required for performance reasons. Together with a second trick, the whole system is much faster as one would guess: This trick is to have two special activities: "beginning of time" (lowest possible date) and "end of time" (highest possible date). This allows to greatly simplify the queries, because deleted_activity now always has a valid value. Life objects are simply deleted at the end of time.