Strolch: Tutorial Model

Previous: Configuration Next: CRUD Books

Looking back at our functionality, we can list the following entities that need to be modelled (We'll go into detail further down):

Book → books can be orderd
UserCart → we want to store the cart of the user
Account → we need to know where to send the orders
PurchaseOrder → we need to know what was ordered and keep track of its state
FromStock → we want to use activities to implement the process of an order

In Strolch we model entities by defining the element as a template. Thus in the templates.xml file we can add the templates with the following content:

Book

<Resource Id="Book" Name="Book Template" Type="Template">
  <ParameterBag Id="parameters" Name="Parameters" Type="Parameters">
    <Parameter Id="description" Name="Description" Type="String" Value="" />
    <Parameter Id="quantity" Name="Quantity in Stock" Type="Integer" Value="0" />
  </ParameterBag>
</Resource>

Account

<Resource Id="Account" Name="Account Template" Type="Template">
  <ParameterBag Id="parameters" Name="Parameters" Type="Parameters">
    <Parameter Id="user" Name="User" Type="String" Value="" />
    <Parameter Id="firstName" Name="First Name" Type="String" Value="" />
    <Parameter Id="lastName" Name="Last Name" Type="String" Value="" />
    <Parameter Id="email" Name="E-Mail" Type="String" Value="" />
  </ParameterBag>
  <ParameterBag Name="Address" Id="address" Type="Address">
    <Parameter Id="phone" Name="Telephone Number" Type="String" Value="" />
    <Parameter Id="street" Name="Street" Type="String" Value="" />
    <Parameter Id="city" Name="City" Type="String" Value="" />
    <Parameter Id="zip" Name="Postal Code" Type="String" Value="" />
    <Parameter Id="country" Name="Country" Type="String" Value="" />
  </ParameterBag>
</Resource>

UserCart

<Resource Id="UserCart" Name="UserCart Template" Type="Template">
  <ParameterBag Id="books" Name="Books" Type="Book">
    <!-- Parameter Id="bookId" Name="Book reference" Type="Float" Value="0" / -->
  </ParameterBag>
  <ParameterBag Id="relations" Name="Relations" Type="Parameters">
    <Parameter Id="account" Name="Account" Type="String" Interpretation="Resource-Ref" Uom="Account" Value="" />
  </ParameterBag>
</Resource>

PurchaseOrder

<Order Id="PurchaseOrder" Name="PurchaseOrder Template" Type="Template" State="Created">
  <ParameterBag Id="books" Name="Books" Type="Book">
    <!-- Parameter Id="bookId" Name="Book reference" Type="Float" Value="0" / -->
  </ParameterBag>
  <ParameterBag Id="relations" Name="Relations" Type="Parameters">
    <Parameter Id="account" Name="Account" Type="String" Interpretation="Resource-Ref" Uom="Account" Value="" />
  </ParameterBag>
</Order>

FromStock

<Activity Id="FromStock" Name="From Stock Template" Type="FromStock" TimeOrdering="Series">
  <ParameterBag Name="objectives" Id="Objectives" Type="Objectives">
    <Parameter Name="Duration" Id="duration" Value="PT1MS" Type="Duration" />
  </ParameterBag>

  <Action Id="validate" Name="Validation of order" Type="Use" ResourceType="Validation" ResourceId="validation" />

  <!-- for each book we do a consume, i.e. reduce the stock quantity -->
  <Action Id="Consume" Name="Consume Template for book" Type="Template">
    <ParameterBag Id="parameters" Name="Parameters" Type="Parameters">
      <Parameter Id="quantity" Name="Quantity" Type="Float" Value="0" />
    </ParameterBag>
  </Action>

  <Action Id="package" Name="Packaging of PurchaseOrder" Type="Use" ResourceType="Packaging" ResourceId="packaging" />
  <Action Id="send" Name="Sending of package" Type="Use" ResourceType="Sending" ResourceId="sending" />

</Activity>

Let's explain a few things:

The Book entity is a Resource object and only contains the description and the current quantity in stock.
The Account entity is a Resource and contains the address and further details of the user, and with the user parameter the username is defined, thus referencing the real user.
The UserCart entity is a Resource and has a reference to the account Resource. Note how the reference is done using a StringParameter, where Interpretation, UOM and the value is set in a specific manner.
The UserCart entity is a Resource and references books using a special ParameterBag with the type set to Book, the actual type of the book entity. Each Parameter is of type Float and the ID of the parameter is the ID of the book, and the value is the quantity that the user would like to purchase. There will only be one cart per user/account.
The PurchaseOrder entity is an Order object, and is basically a copy of the UserCart entity. This is the confirmed purchase order for the contents of a cart, and can then be used for reports on how much of which book was sold.
The FromStock entity is an Activity object and defines the process we will go through when delivering a purchase to a user. Note how the activity has a ParameterBag objectives with a duration parameter. This defines globally for this activity how long each Action should execute. This can be overridden in each Action and can help to plan how much effort goes into the delivering of each PurchaseOrder.
Further note how the activity has three special actions (validate, package and send) on which a ResourceType and ResourceId are defined. Actions are always performed on a Resource, as the referenced Resource defines the behaviour of the action through defined Policy objects.
For each book which will be purchased, an Action will be created of type Consume. In the template this is defined by a template Action with the id Consume and will later be changed accordingly.

Since we are referencing resources from actions in the activity, we need to add these as well, but not as templates. They can be added to the defaultModel.xml file:

<Resource Id="validation" Name="Validation Resource" Type="Validation">
  <Policies>
    <Policy Type="ExecutionPolicy" Value="key:ValidationExecution" />
    <Policy Type="ConfirmationPolicy" Value="key:DefaultConfirmation" />
  </Policies>
</Resource>

<Resource Id="packaging" Name="Packaging Resource" Type="Packaging">
  <Policies>
    <Policy Type="ExecutionPolicy" Value="key:PackagingExecution" />
    <Policy Type="ConfirmationPolicy" Value="key:DefaultConfirmation" />
  </Policies>
</Resource>

<Resource Id="sending" Name="Sending Resource" Type="Sending">
  <Policies>
    <Policy Type="ExecutionPolicy" Value="key:SendingExecution" />
    <Policy Type="ConfirmationPolicy" Value="key:DefaultConfirmation" />
  </Policies>
</Resource>

What should now be noted by these three new Resources is that they have Policy definitions:

ExecutionPolicy → defines how an action on this resource is executed by referencing an ExecutionPolicy implementation.
ConfirmationPolicy → defines behaviour to be performed on every state change of an action being performed on this resource by referencing an ConfirmationPolicy implementation.

Currently these resources reference policies which don't exist. We will resolve this issue later, when we implement the execution of the activity.

This concludes the model definition. In the next step we'll start creating services and commands for our model.

Previous: Configuration Next: CRUD Books

Tutorial: Model