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Understanding SIU Workflows

The Mac OS X v10.5 version of SIU introduced an entirely new way to create custom network disk images to suit your specific deployment needs, through an easy-to-use graphical interface that allows you to define custom images and system deployment workflows.

About Automator Actions

To implement a flexible network disk image customization system, SIU uses Mac OS X’s Automator technology. The Automator application, located in the /Applications folder, allows you to automate repetitive application tasks. This technology is based on AppleScript, a much older technology. AppleScript is a very powerful application scripting language, but like any computer programming language, it has a learning curve. With Automator, even novice computer users can take advantage of the powerful automation features of AppleScript without having to know how to write code.

Automator accomplishes its work through Automator actions, each of which presents a small graphical interface that allows you to perform a very specific automated task in a specific application. You can use these actions as building blocks, combining multiple Automator actions into an ordered list to build an Automator workflow that can be used to perform a repetitive task.

In many cases the order of the Automator actions in a workflow matters, not only because it defines the order in which actions take place, but also because adjacent actions can communicate to one another through inputs and outputs. For example, an Automator action for the Finder can mount a disk image volume, but first it requires input from another action that identifies the specific disk image to mount. The first action selects the disk image file and outputs that information so the action that mounts the disk image knows which image to mount. The following figure shows a simple example of an Automator workflow. Notice the input-output connection between the two actions.

Automator has proved so successful in simplifying complex tasks in standard applications that Apple based the creation of network disk images on this technology. Included with SIU is a suite of Automator actions tailored to the creation of custom network disk images. By using the same simple technique of ordering Automator actions into an Automator workflow, you can create a custom workflow-generated network disk image, which previously would have required a significant amount of skill and time to manually configure and code.

Creating Images with SIU Workflows

System Image Utility in Mac OS X v10.6 includes 11 Automator actions for the creation of custom network disk images. Although you can access the SIU-related Automator actions from the Automator application, an easier method is to start with SIU to build your workflow-generated network disk images. Within SIU, simply click the Customize button to enter SIU workflow mode. The workflow mode will open with the two primary SIU actions already in place, Define Image Source and Create Image.

These two actions are the primary SIU actions required for creating network disk images. The Define Image Source action allows you to select the system image source, and the Create Image action allows you to configure the network disk image settings. These two primary SIU actions must always be the first and last actions for any workflow that builds a network disk image. All other SIU actions are optional and can be placed in between the two primary SIU actions. Think of the two primary actions, Define Image Source and Create Image, as bookends for the network disk image creation process.

You may have noticed that the SIU workflow mode also opens an Automator Library window showing you all the SIU-related Automator actions. Selecting an action from this list shows a brief description of the action at the bottom. To incorporate an action into a workflow, simply drag it to where you want it in the workflow.

Using Automator instead of SIU allows you to incorporate other non-SIU actions into a workflow. Just make sure not to interrupt the connection flow between the primary “bookend” SIU actions and the other optional SIU actions; otherwise your workflow may fail to complete the image build. Note that if you want your workflow to perform other tasks besides building a network disk image, you can place those actions before or after your set of SIU actions. For example, you could add actions after the Create Image action that mount a server share and then copy the newly created network disk to the appropriate folder on the NetBoot server.

Ultimately your goal shouldn’t be just to build a network disk image; your goal should be to develop workflows that can automate building images for you now and in the future. This is why there is a Save button next to the Run button at the bottom of SIU. Once you build a workflow, save it. In the future, use your previous workflows as building blocks for new, possibly more sophisticated workflows.

The workflow files saved by SIU are actually formatted as Automator workflows, so they open directly in Automator when double-clicked on in the Finder. This is no accident, as you’ll find that Automator provides a more complete interface for building more sophisticated workflows. Using Automator you can combine SIU actions with other non-SIU actions, use variable substitution, integrate with other applications using the Services menu, and even other scripting technologies including full AppleScript and shell scripting.

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