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During the last video,
we looked at a bunch of principles,

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including the separation of concerns,
single responsibility, and loose coupling.

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All of that can seem really
abstract without an example.

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Let's now take a peek at what it means for
us in Giflib.

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[SOUND] In Giflib, we'll split our
application into three layers,

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the web layer, data access layer,
and service layer.

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[SOUND] The web layer will consist of the
controllers we've already started as well

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as anything relating specifically
to serving web content.

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The data access layer we'll name DAO,
which stands for Data Access Object.

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Here we'll write one DAO class for
each entity class.

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And its sole purpose will be to
interact directly with Hibernate.

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This will be the place where we
code all of our CRUD operations.

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Finally, we'll have a service layer.

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[SOUND] This layer will receive requests
from a service client, which in our case

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is a controller, and it'll make any
calls to the DAO that are necessary.

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This layer could also
perform any computations or

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processing that are outside
the realm of our model objects.

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Our layers will be structured as
packages and we'll keep relationships

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between the packages tightly
controlled and loosely coupled.

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What this means is that any time there's
an interaction between the layers,

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that interaction will take place
via interfaces, not classes.

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As we get the structure in place,
you may see a redundancy in code.

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We'll create an interface and

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a class implementing that interface for
each entity in our application.

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Know that this apparent repetition
is in our best interest as we code

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an application that is more maintainable,
extensible, reusable, and testable.