Databases Reference
In-Depth Information
FIGURE B.28
Data model levels—analogy.
The high-level data model is represented by ovals connected by lines. The high-level data model
is where the major subjects of the corporation reside. This level of the data model represents the most
abstract aspects of the healthcare environment. The lines that connect the high-level subjects depict a
relationship between the subject areas. Oftentimes the high-level data model is called an ERD, or an
entity relationship diagram.
The mid-level data model is derived from the high-level model. The mid-level data model consists
of a much more detailed description of the data, the grouping of the data, and the relationships of the
data to each other. Each high-level subject area turns into its own mid-level data model. The mid-level
data model is often called the DIS, or data item set. In the diagram the cluster of boxes in the center
of the diagram represents the mid-level data model.
The low-level data model is the place where physical characteristics appear. The low-level data
model is the first draft of the physical database design. In the diagram, the green box that is full of
attribute definitions represents the low-level data model.
The relationship of the different levels of the data model can be described in terms of an analogy.
Figure B.28
shows the analogy.
The high-level data model is analogous to a globe (that represents the Earth). The mid-level data
model is analogous to a map of the state of Texas. The low-level data model is analogous to the city
map of Dallas, TX. Note that there is a relationship between each level of modeling. The state of Texas
can be recognized in the globe. And the city of Dallas can be recognized inside the map of Texas.
