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    <p>Mike,</p> <p>your question is really cool, I like it. Firstly, feel free to experiment a bit - each and every project is different, so there's no single rule, which fits everywhere. That's why I would suggest just leaving DAL to LINQ 2 SQL. this great tool will handle it, you don't have to worry. Secondly - you mentioned 3 Tier Architecture, but why isn't there place for the Model? Since all models are generated automatically (e.g. SQLMetal), you don't have to worry about mappings either. So, if you're not bored yet, let me answer all of your 3 questions:</p> <ol> <li><p>Skip DAL and observe your project carefuly - if you have a feeling, that it's lacking this layer - add it (it will contain LINQ2SQL queries). And the second part - you can return whatever you wish, but it will be most convenient for you to use IEnumerable&lt;> or IQueryable&lt;> parametrized with your models.</p></li> <li><p>My intuition tells me, that you're going to need WCF - in this case you should be able to wrap whole (yes, that's true) whole business logic in a nice Contract and implement however you wish.</p></li> <li><p>This is the easiest one :) Since your BLL layer is actually an implementation of some Contract (Interface), you can design that Interface to provide you with all data you need. For example:</p></li> </ol> <p>Contract/Interface:</p> <pre><code>IEnumerable&lt;User&gt; GetTallUsersOver40(); IEnumerable&lt;User&gt; GetShortUsersOver60(); ... </code></pre> <p>And that 'all the layers' you were talking about shrink to a single LINQ2SQL query execution. If you need more logic - place it in this layer.</p> <p>I want to use MVVM, what now? The answer is simpler than you think - just prepare your views and view models and simply consume your BLL Contract/Interface implementaion. </p> <p>Please ask if you have further questions!</p>
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    1. COSo is the "Model" in Model-View-ViewModel essentially the BLL that I will wrap in WCF?
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    2. CONot exactly. Please think of a Model like of a separate layer made just to map (or literally "model") your persistent data. In short: Model is a set of classes designed for modeling your database. Since LINQ 2 SQL does modeling for you (this is simply brilliant), please don't worry about this - you have all modeling classes provided :) if you have further questions - please don't hesitate to ask them.
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    3. COHmm... I guess I'm having trouble envisioning the layers. Let's see if I have this right. On the top, we've got the View which has an associated .cs file that ideally no code goes in there. The view binds to the ViewModel which is essentially an adapter for the View. (Now this is where I start getting lost), since the model is taken care of by LINQtoSQL, Do i put a reference/connect to the WCF BLL in each ViewModel? And then lastly, have the BLL reference the DAL? And the dataContext goes in the DAL?
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