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2018-02-08-feature-definition.html
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<h1 class="post-title" itemprop="name headline">Introducing Feature Definition</h1>
<p class="post-meta">Published by <img src="https://www.gravatar.com/avatar/4bc2f02eb142f56b3a2f1e9ff49b3629?s=135" alt="A photo of Jürgen Fickel" style="width:50px;border-radius:50%;display:inline-block;margin-right:5px;" /><span itemprop="author" itemscope itemtype="http://schema.org/Person"><span itemprop="name"><a href="https://github.com/jufickel-b" target="_blank">Jürgen Fickel</a> </span></span> on <time datetime="2018-02-08T00:00:00+00:00" itemprop="datePublished">Feb 8, 2018</time> - Tags:
<a href="tag_blog.html">blog</a>
</p>
</header>
<div class="post-content" itemprop="articleBody">
<p>Brace yourselves, <a href="https://eclipse.org/vorto">Eclipse Vorto</a> is going to be integrated with Ditto.</p>
<h2 id="rationale">Rationale</h2>
<p>By now you most probably represented your devices as <em>things</em> with <em>features</em>.
This is indeed the proper way to do it.
This approach is flexible and easy so far.</p>
<p>But wouldn’t it be nice to have the possibility of providing an explicit schema for the digital twins of your devices?</p>
<p>This is where Eclipse Vorto enters the game.
Vorto enables you to define <em>information models</em> and <em>function blocks</em> which would be mapped to <em>things</em> and <em>features</em>
in Ditto.</p>
<p>To make a feature aware of a schema we have extended feature by a <em>definition</em>.
A feature definition is a means of describing the type of a feature, thus enabling the validation the integrity of
a feature’s properties.</p>
<figure><img class="docimage" src="images/pages/basic/ditto-thing-feature-definition-model.png" alt="Feature Definition Model" style="max-width: 250px" /><figcaption>One Thing can have many features. A feature may conform to a *definition*</figcaption></figure>
<p>Technically, a definition is an array of identifier strings each of which having the form
<code class="language-plaintext highlighter-rouge"><namespace>:<name>:<version></code>.</p>
<p>A fully-fledged JSON representation of a feature with a definition is shown below:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="nl">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"definition"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="s2">"com.mycompany.fb:Lamp:1.0.0"</span><span class="w"> </span><span class="p">],</span><span class="w">
</span><span class="nl">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"configuration"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="nl">"location"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"longitude"</span><span class="p">:</span><span class="w"> </span><span class="mf">34.052235</span><span class="p">,</span><span class="w">
</span><span class="nl">"latitude"</span><span class="p">:</span><span class="w"> </span><span class="mf">-118.243683</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="nl">"status"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="nl">"color"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="nl">"red"</span><span class="p">:</span><span class="w"> </span><span class="mi">128</span><span class="p">,</span><span class="w">
</span><span class="nl">"green"</span><span class="p">:</span><span class="w"> </span><span class="mi">255</span><span class="p">,</span><span class="w">
</span><span class="nl">"blue"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>For diving deeper into feature definitions, please have a look at <a href="basic-feature.html#feature-definition">Basic concept - Feature Definition</a>.</p>
<h2 id="validation">Validation</h2>
<div class="alert alert-danger" role="alert"><i class="fa fa-exclamation-circle"></i> <b>Warning:</b> Yet Ditto does not use definition to validate features by itself.</div>
<p>However, nothing can stop you from enforcing types by yourself:</p>
<ol>
<li>Use the Ditto generator to generate JSON schema files from your Vorto
model(s).</li>
<li>Identify the schema files to be used by the Feature definition identifiers.</li>
<li>Validate the JSON representation of your feature using the JSON schema before sending it over the wire.</li>
</ol>
<h2 id="example">Example</h2>
<p>Please find more information and an example at <a href="basic-feature.html#feature-definition">Basic concept - Feature Definition</a>.</p>
<p><br />
<br /></p>
<figure><img class="docimage" src="images/ditto.svg" alt="Ditto" style="max-width: 500px" /></figure>
<p>–<br />
The Eclipse Ditto team</p>
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