Topics: Data modeling, Data model, Entity-relationship model Pages: 6 (2947 words) Published: October 10, 2014
Some Types and Uses of Data Models

Different Types of Data Models
One of the things you often find people arguing about is what a data model is, and what it is for. Here’s one of the secrets of analysis: when you find people arguing passionately about something, try to discover why they are both right. So it is with data models. Data models have many purposes. These cause differences in both style and content, which can cause confusion, surprise, and disagreement. This section looks at some different types of data models (I do not claim necessarily to have exhausted the possibilities) and how their purposes might lead them to differ for nominally the same scope. A particular data model may be of more than one of the types identified. Physical Data Model

A physical data model represents the actual structure of a database—tables and columns, or the messages sent between computer processes. Here the entity types usually represent tables, and the relationship type lines represent the foreign keys between tables. The data model’s structure will often be tuned to the particular needs of the processes that operate on the data to ensure adequate performance. It will typically include: Restrictions on the data that can be held

Denormalization to improve performance of specific queries
Referential integrity rules to implement relationship types
Rules and derived data that are relevant to the processes of the application(s) the physical data model serves Logical Data Model
There is a range of views on what a logical data model is. So I will start by talking about how I see them and then mention the divergences that I have noticed. A logical data model is a fully attributed data model that is fully normalized. Fully attributed means that the entity types have all the attributes and relationship types for all the data that is required by the application(s) it serves. It may include: Restrictions on the data that can be held

Rules and derived data that are relevant to the processes of the application(s) the logical data model serves The main difference I see from this in practice is that many data models that are described as logical actually have some level of denormalization in them, particularly where change over time is involved. A logical data model might relate to a physical data model, but this is not the only possibility. For example, with a software application, it would be quite appropriate for a logical data model to be developed of the user view of the application through the screens, and/or the computer interfaces to and from the application. This might be considerably less flexible than the underlying database, with restrictions imposed either by the application code, or by the configuration of the application. It should be clear from this description that a physical data model can also be a logical data model, provided it does not include any denormalizations. Conceptual Data Model

As with logical data models, there are some differing opinions about what a conceptual data model is. So again, I will state the way that I understand the term and then identify some key variations I have noticed. A conceptual data model is a model of the things in the business and the relationships among them, rather than a model of the data about those things. So in a conceptual data model, when you see an entity type called car, then you should think about pieces of metal with engines, not records in databases. As a result, conceptual data models usually have few, if any, attributes. What would often be attributes may well be treated as entity types or relationship types in their own right, and where information is considered, it is considered as an object in its own right, rather than as being necessarily about something else. A conceptual data model may still be sufficiently attributed to be fully instantiable, though usually in a somewhat generic way. Variations in view seem to focus on the level of attribution and therefore...
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