How the Number property is used in structures

The Number property automatically shows each object's level and sequence within a Systems Engineering structure. For example, assume that objects A, B, and C occupy the first level, directly under the top object in the structure. Also, each object has three children at the next lower level.

In this example, the Number column values are:

• 1 for object A, with 1.1, 1.2, and 1.3 for its children
• 2 for object B, with 2.1, 2.2, and 2.3 for its children
• 3 for object C, with 3.1, 3.2, and 3.3 for its children

The Number column values are adjusted automatically when objects move up and down in a structure through:

• Promote and demote structure elements to higher and lower levels.
• Move structure elements up and down within their current levels.
• Add or remove structure elements.
• Manually updating the numbers directly.

Multiple levels in a structure allow flexibility in the organization of requirements and models. For example, all requirements can occupy the top level, directly below the requirement specification. Or, requirements can be structured in a hierarchy, in which the levels convey relationships among the requirements.

Working with hierarchical structures in Systems Engineering is similar to working with numbered paragraphs in Word's outline view. A given structure element may occupy the highest level, as a sibling of all other structures at level 1. Or, it may occupy a lower level, as a child of the structure element at the next higher level. In turn, a child structure element may also be a parent of children at even lower levels.

Structure elements can be organized in multiple levels of parents, children, and siblings. The Number column shows this hierarchy, with a plus sign (+) for an item that has one or more children at lower levels.

You can move items to higher and lower levels, changing their relationships to other items in the structure. When you move a parent item, you also move its direct children and lower-level descendants.