add decision log for table relationships

models/DECISIONLOG.md

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+## Relationships between Task, Problem, Incident, and Change Request tables in ServiceNow
+
+Tasks, Problems, Incidents, and Change Requests are related in ServiceNow. To add clarity to the logic in our models, below are summaries of each table and additional information regarding the relationship between the tables.
+
+### Tables
+#### Tasks:
+
+- The base table for various task types, including Incident, Problem, Change Request, and more. Contains common fields and functions as a central point for task management.
+
+#### Incidents:
+
+- Extends from Tasks. Represents a reported issue or service disruption. Can be related to Configuration Items (CIs) and assigned to specific groups or individuals. 
+- Can be caused by and therefore linked to Problems. It can also be waiting on a Change Request. 
+
+#### Problems:
+
+- Extends from Tasks. Represents the underlying cause of one or more incidents. Therefore they can be linked to Incidents and may involve a root cause analysis.
+
+#### Change Requests:
+
+- Extends from Tasks. Represents a proposed change to the IT infrastructure or services. Can be related to CIs and undergoes an approval process. A Change Request can result from a Problem or Incident. 
+
+### Table Relationships:
+
+Incidents and Problems are often related to Tasks through a parent-child relationship. An Incident or Problem task can have related sub-tasks. All Incident and Problem tasks exist in the main Task table. An Incident can be caused by more than one Problem, and a Problem can cause more than one Incident. Therefore the relationship is many-to-many.
+
+Change Requests may also have a parent-child relationship with Tasks when tasks are created to implement the changes proposed in the change request. 
+
+A Change Request can result from multiple Problems or Incidents. Multiple Change Requests can be created from a Problem or Incident. Therefore the relationship is many-to-many.
+
+You can create a Problem or Change Request from Incident, or, Change Request from Problem, or can create an Incident from Change Request in cases where it is required.
+
+
+### Example Relationship:
+
+-  Suppose a user creates a Incident for an issue and then 100 other users create an Incident with the same issue. You would create a Problem for all the incidents, therefore linking all Incidents to one Problem. Once the problem record is resolved, it will close out all of the incidents as well.