# Synchronous Technology In Solid Edge ST3 – Part 2

<< Part 1

In this part I will explain the concept of ordered features and synchronous features. Siemens PLM calls the features created by the traditional method of history based parametric modeling as ordered features, simply because the order in which they appear matters. For example, consider this very simple model created by extruding a square to a Base protrusion, then protruding a circle on its top face and cutting a square also on its top face, cutting both protrusions.

This is what the feature tree looks like

Now let’s see what happens if I change the order of the features in the tree. Say I move the circular protrusion after the square cutout, the feature tree looks like this.

And the model becomes this.

As you can see the result is now very different. The circular protrusion is not cut by the square cut because it did not exist at the time the square was being cut. Since we moved the circular protrusion after the square cut in the feature tree it got added later which resulted in different geometry. So this goes to show that the order in which the features exist in the feature tree is important and hence Siemens PLM has decided to call these features “ordered”. Notice the yellow bar titled “Ordered” in the tree above.

Now suppose I had modelled the same part creating the same features but without history, that is, using Synchronous Technology. The features created this way are called “synchronous” features. This is what the feature tree would look like. Notice the yellow bar titled “Synchronous”.

As you can see, we have a Base feature, then Protrusion and finally Cutout, same like in the ordered feature tree mentioned above. The model looks like the first image above. Now suppose I reorder the features in the tree and move the Protrusion feature after the Cutout this is what the feature tree will look like.

The model still looks like the first image above. To understand why the geometry is not altered like it was in the previous method of modeling, you need to understand what synchronous features are.

To put it simply, a synchronous feature is a merely a collection of faces that define the shape of a feature. So the Protrusion synchronous feature is basically a collection of the faces highlighted in the image below.

The Cutout synchronous feature is a collection of faces highlighted in the image below.

So it really does not matter where these features lie in the synchronous feature tree. In fact, I could even place the Cutout synchronous feature before the Base synchronous feature and the geometry would still remain the same.

You can consider the synchronous feature tree as a collection of all the faces of the model, just that they are grouped by features that use them. So if you want to know which faces make up the Base feature they are shown highlighted in the following image.

For this simple model, if you stitch together all the individual faces of all the synchronous features you will end up with a closed solid body. Hence the term synchronous because all the features in the model are computed at the same time, as opposed to one after another like in the case of the ordered feature tree.

Part 3 >>