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Cloning this repository produces a large set of eclipse friendly projects that can be imported into eclipse. 

Interfaces and Abstract classes to Extend

Loader interfaces must extend the interface org.LexGrid.LexBIG.Extensions.Load.Loader from the lbInterfaces project and implementations of your new interface must also extend the abstract class org.LexGrid.LexBIG.Impl.loaders.BaseLoader in the lbImpl project.  Let's take as an example the Medra loader interfaces and classes as it is a relatively simple implementation:

The extension of Loader is org.LexGrid.LexBIG.Extensions.Load.MedDRA_Loader.java and is found in the lbInterfaces project.  This defines a loader and validation method and creates initialized class attributes name and description.  The name of this interface will eventually be used by the LexEVS extension function to call the loader into existence.  (Loaders are always extensions to LexEVS). 

Implementation Example and Discussion

Call the super constructor in the constructor

Looking at the implementation of this interface in lbImpl, org.LexGrid.LexBIG.Impl.loaders.MedDRALoaderImpl, notice that implementation is kept relatively clean thanks to much of the mechanism of loading into LexEVS is taken care of under the covers by BaseLoader.  It creates a constructor that always calls the BaseLoader constructor, then prevents the use of manifests.  (If you wish you may choose to allow manifest use, since it allows load time manipulation of coding scheme metadata.  Often source files do not provide all that needs to be known about the source.  A manifest file allows values that may not be present in the source, such as copyrights, authoring information, version definition and formal coding scheme name to be added to the load.)

Define the extension

The buildExtensionDescription method provides a background method for the registration of this loader to take place within LexEVS. It should be created the same way for each loader.

Validate the Source (optional)

The validate method is not always implemented, but can and should be when a mechanism exists to insure that this is a correctly structured version of the source.  When source is XML formatted and has a schema or dtd document commonly available for validation, this is a relatively easy process.  However any free text files that do not have any associated java-based validation API, would rely on the developer to create validation functions.  The validation method is not required to create a loader for LexEVS. 

Implement the Abstract Method doLoad() (And possibly override the load() method)

In order to get loading done theory the developer could at this point implement only doLoad by mapping content to a coding scheme object and persisting it before turning control over to BaseLoader which will call the doLoad method and set default load options in its load method and kick off the processes to persist a coding scheme object to the database.  The other option is to implement doLoad and override the load method which sets up end user option choices for the loader.   Most loaders implement the load method, customizing load options to provide to the end user.  In the case of the MedDRA loader, a CUI load option is provided to the end user.

Beyond these methods, where a coding scheme object is passed to LexEVS for processing, the structuring of code is largely and necessarily left up to the developer.  However a few common patterns are fairly consistent in this implementation.  Generally speaking, there is a central mapping class where the coding scheme object is built.  Other classes, when necessary, are supportive to this central class. 

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