Planning parent-child relationships
When setting the key structures for parent-child relationships - it can be helpful to fill in a table like the following example:
Here a SECTION may contain EMPLOYEEs.
An EMPLOYEE may have associated SKILLs.
An EMPLOYEE may have associated DOCUMENTs.
| BO | ROLE | AKey1 | NKey1 | AKey2 | NKey2 | AKey3 | NKey3 | AKey4 | NKey4 | AKey5 | NKey5 |
| SECTION | PARENT | #DEPTMENT | Implicitly used by parent | #SECTION |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
| EMPLOYEE |
CHILD (of SECTION) |
Must be same as parent’s #DEPARTMENT value | Implicitly used by parent - so must have same default value. | Must be same as parent’s #SECTION value | Implicitly used this by child | #EMPNO – should make this child unique within this DEPARTMENT and SECTION |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
| SKILL |
CHILD (of EMPLOYEE) GRANDCHILD (of SECTION) |
Must be same as parent and grandparent’s #DEPARTMENT value | Implicitly used by parent and grandparent - so must have same default value. | Must be same as parent and grandparent’s #SECTION value | Implicitly used by parent - so must have same default value. | Must be same as parent’s #EMPNO value | Implicitly used by this child | #SKILLCODE – should make this employee’s skill unique within this DEPARTMENT and SECTION and EMPLOYEE |
Free for children to use |
Free for children to use |
Free for children to use |
| DOCUMENT |
CHILD (of EMPLOYEE) GRANDCHILD (of SECTION) |
Must be same as parent and grandparent’s #DEPARTMENT value | Implicitly used by parent and grandparent - so must have same default value. | Must be same as parent and grandparent’s #SECTION value | Implicitly used by parent - so must have same default value. | Must be same as parent’s #EMPNO value | #DOCNUMBER – should make this employee’s document unique within this DEPARTMENT and SECTION and EMPLOYEE |
Free for children to use |
Free for children to use |
Free for children to use |
Free for children to use |
The parent-child association rules that you must follow are:
- Any child business object must have exactly the same keys as its parent plus one or more keys to uniquely identify itself.
- A child business objects can use the free keys not used by its parent. They can only start immediately after the last parent key used (real or implicit) working from left to right in the key structure.
You might also consider condensing key structures when your theoretical planning is finished – the keys are programmatic and not visible to end-users.
For example: by choosing #DEPTMENT + “-“ + #SECTION as the AKey1 value in the table above you could condense it towards the left by two columns - freeing up a considerable amount of key space.