Easier building complex applications in Joomla! by adding a mapping layer between the domain model and the database. Some of this might be useful to improve Joomla!'s core.
While building custom Joomla!-extensions I often encountered difficulties implementing one-to-many and many-to-many relations.
Joomla! uses lists and items, where a list relates to a database table and an item to a record in that table. Because the underlying relational database is normalised, fields are atomic: contain only one value. In reality (in the domain) a person can have multiple addresses, an order can have multiple orderlines, a posting can have several comments, a product can have several images etc. Often, fields in our entities are not atomic, but can have collections of values. If we stay close to the one-to-one mapping of lists/items and database tables, as Joomla! natively does, it soon becomes messy when modelling more complex relationships. But if we use a mapping between the objects in our domain model and the database, we can easily use non-atomic fields. The same holds for inheritance mapping: a parent class and child classes can be mapped to a relational database in several ways. The Unified Content Model (UCM) is an example of class table inheritance mapping, where the superclass (core_content) has its own table, as do the subclasses. This opposed to the currently used concrete table inheritance, where every content-type maps to one table.
Fortunately this Object Relational Mapping has allready been extensively elaborated. No need to reinvent this wheel. In this presentation I'll show how I used Doctrine ORM for it. And I'll show how this could be used to improve Joomla!'s core.