Comprehensive and Detailed 150 to 250 words of Explanation From Workday Record-to-Report/Course Guide/topics:

When creating a custom report, the report writer must select a data source immediately after providing the unique report name and report type. The data source establishes the population of records available to the report, determines the primary business object, and controls which fields, related business objects, filters, and prompts can subsequently be configured. Selecting the correct data source is therefore a structural decision, not merely a display choice.

Report fields are added only after Workday knows which business objects and field families the data source exposes. The primary business object is derived from or associated with the chosen data source rather than independently selected as the first required input. Related business objects extend the report through relationships from that primary object and likewise cannot be defined before the source population exists. An indexed data source may additionally provide predefined data source filters for performance and security. Consequently, Data source is the required answer. A poorly selected source can cause missing fields, duplicate rows, inefficient processing, or an inappropriate security context, so the report writer should evaluate the business question and expected record grain before continuing with columns, filters, sorting, prompts, and sharing.

Official Workday reference: Workday Education - Workday Reporting ; topics: custom report definition, data source, and primary business object.

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