Scenario
Let's have a closer look at the Data Model Definition phase. In this phase you must know the different approaches to define the data model.
There are two ways of deriving the data model: data-source based (bottom-up) and key-figure based (top-down).
DataSource Approach (Bottom-Up)
The question "What can we provide?" drives the bottom-up approach, starting from existing sources. It’s useful for a pilot project.
Determine the relevant DataSources and fields. You can have a look at available BI content and how it maps to the fields you found to InfoObjects. Based on the source information, analyze which BI content objects (upward data flow) are required for the scenario. Then, determine InfoProviders and Queries.
If your project is enterprise resource planning (ERP)-based, or if one of the source systems is an SAP ERP system, the bottom-up approach is recommended. Because the customers already know a lot about the SAP ERP system, they’re keen to have the correct data in SAP BW/4HANA. Therefore, it's easier for an SAP BW/4HANA consultant to use terms relating to the SAP system, as these terms are familiar to the customer.
Key Figure-Based Approach (Top-Down)
The top-down approach is driven by the question, "What do you want?", starting from the desired KPIs.
A key figure-based approach involves the following steps:
Get a clear idea of your requirements, especially key figures.
Develop a logical data model without technical details.
Derive an SAP HANA calculation view-based model, or an SAP BW/4HANA model with technical details. In an SAP BW/4HANA model, define DataStore Objects (advanced) for transactional data, and InfoObjects for master data (attribute relations, texts, and hierarchies), and CompositeProviders to combine them.
At the end, you can check for suitable BI content. Find relevant sources for the required Queries, and compare the properties of BI content objects with your model design.
Mixed Strategy
The main approach in a reporting project is a mixed approach. Similar to a top-down approach, start from the business process and identify its KPIs. Then look for possible sources. Identify how you must transform basic key figures. Look for corresponding BI content. If the search for corresponding key figures is unsuccessful, try a bottom-up approach. If the required fields are missing, check whether they can be added: that is, whether they exist in the system. In a mixed scenario, the top-down and bottom-up scenarios aren't completely separate from each other. Simultaneous use of both scenarios makes the modeling process more efficient.
Another option is to start with a top-down approach and add new objects according to a bottom-up approach.
It’s important to understand the business basis and background of the model. A technical description alone won't lead to a complete result.
Proposal for a Top-Down Approach
Let's take a specific approach and have a look at the steps. We discuss a top-down approach to derive the data model.
Watch this video to learn about the steps in the proposed approach to create a data model.
In the next lesson we have a detailed look at these steps.