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Cradle from 3SL, the complete Model Based Systems Engineering Toolsuite, specialising in requirements management, requirements capture, model based systems engineering and for systems engineering software, support and consultancy, the logical choice: Cradle from 3SL.

January 2010 [Cradle 6.1]

Building Item Hierarchies

Hierarchies are seldom created in a single operation. It is more usual for a hierarchy to be created interactively, gradually developing the hierarchy item by item.

Cradle makes this process very simple. The hierarchy can be extended by selecting a node in the tree (or in a list or table) and either right click and choose New and the appropriate menu option:

Or select the item in the tree (or list or table) and select Item → New and the appropriate menu option:

The options to build hierarchies of items are:

  • Child – creates a child of the selected item, by:
    • Creating an item of the same type
    • Recording a hierarchical number, either in its Number attribute (if the item is not auto-numbered) or in the Key or a category code (if the item is auto-numbered, as defined in the project schema)
    • Creating a cross reference from the selected item to the new child item
  • Sibling – creates a new item that is a child of the same item as the current item, by:
    • Creating an item of the same type
    • Recording a hierarchical number, as above
    • Creating a cross reference from the selected item’s parent to the new item
  • Hierarchy – creating a hierarchy of N levels of items with M items at each level below the selected item, by repeatedly performing the steps listed for Child above

To be able to use these facilities, you will need a Cradle user profile (a login account) which has CREATE_ITEM and CREATE_XREF privileges, since these operations create both items and cross references.

As an example, to create the SBS for a laptop:

The sequence of operations would be:

  1. Select the SBS item type in the Project sidebar:



  2. Right click and choose New → Item… and enter Laptop as the Name and 1 as the Key:



  3. Double click the SBS item type to see the new item in the tree:



  4. Select the SBS item, right click and choose New → Child… and enter Hardware as the Name of the child, we don’t need to set a Link Type for the cross reference to be created because Cradle will automatically include the valid type(s) in the dialog based on our project schema:



  5. Repeat for the second child Software and double-click the Laptop SBS item to see the children:




    6. and you can see that Cradle is automatically assigning:
    • A unique ID for each SBS item: SBS-1, SBS-2 and SBS-3, held in these items’ Number attributes
    • A hierarchical number, based on the initial value 1 that we manually entered into the Laptop item’s Key

  6. Each new SBS item is opened in a form when you create it, so periodically select the:

    button in the top-right corner of the pane, and choose Close All Tabs to close all of the forms:



  7. Repeat the process to add the children for the Hardware and Software item, to produce the final System Breakdown Structure hierarchy:



If you wish, you could try creating this hierarchy using the New → Sibling operation. This is very similar to the process just described, except that having created the first child, you display it in the tree, select it and then create the other children (its siblings) using the New → Sibling operation.

Creating a new item as a child of its parent with New → Child and creating the item as a sibling of an existing child of this parent with New → Sibling produce identical results in the database. It is a personal preference which method you use.