Dear Mikael, since I initially started the discussion, I explain what my needs/opinions are.
A good persistence-layer reflects the classes which want to be persistent. The classes do not need to know what DB-vendor is involved. There will be no db-vendor specific code in the main application, the db-vendor specific code will be in the persistence layer There is an abstraction between DB-vendor and classes that want to be persistent. Post-relational-db's, XML-db's, relational DB's of all vendors should be accessible over the same code-interface. The purpose doesn't matter, the complexity doesn't matter. This concept is scaleable, just changing a few strings makes the application work against another database, of another or same vendor, on another or same machine. It makes an application fit to work on a notebook with a small DB, as on a remote DB-server, the application, same code, different branch below in persistence layer, which is already generic programmed against most databases and situations. That is what I mean, when talking about a persistence layer Mikael Nystr?m wrote: >Dear all, > >I think before we discuss how we are going to build a persistence layer we >need to discuss how we are going to use it. Is it to support a simple >electronic healthcare record application which only collects basic >information, print the information on a computer screen or on a paper on a >small center for primary health care? Or is it to support an information >system for electronic healthcare record information used everywhere on a >large hospital (or a country!) and where the system is able to amongst >others support data intensive applications like real time data driven >decision support systems? If it is the first case the persistence layer can >be built in many different ways and where some of the ways are simple and >fast to build. If it is the second case there are much fewer ways to build >the persistence layer and probably none of them are simple and fast to >build. > > Regards, > Mikael > >Mikael Nystr?m >M Sc in Computer Science and Engineering >Ph D student in Medical Informatics >Department of Biomedical Engineering >Link?ping University > > > > > >
