I am implementing a database search algorithm which searches over many collections in a MongoDB and returns optimized results based on the state of the entire database. I have no problems with the implementation, but the nomenclature and how I should structure the file system is bugging me. Where in the model-view-controller pattern should I place read only operations? Is it a service? It has a controller but I hardly think it satisfies the criteria to be a model.
This question is extremely language dependant and the features that exist within that language. I will speak from a PHP point of view.
Search functions should go into the model, the model backs up as a data provider in the MVC pattern. A single central point from which to dish out instances of it self.
Some MVCs implement what is known as factory classes. They are specifically designed to sit outside of the MVCs normal pattern to be able to provide data: http://en.wikipedia.org/wiki/Factory_method_pattern . As someone who has used this pattern I can say it gets complicated and unmanageable very quickly. That is why I prefer to backup the model as a data provider itself, it merely requires class organisation.