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Difference Between Cardinality and Modality
For understanding the information domain of a problem, there are two data modelling concepts, namely, cardinality and modality. Cardinality and modality are very important for analyzing the data objects, attributes, and relationship structures. The most basic difference between cardinality and modality is that the cardinality is a metric that specifies the number of occurrences of a data object with respect to the number of occurrences of another data object, whereas, the modality specifies whether a data object must participate in a relationship or not.
In this article, we will discuss the important differences between cardinality and modality. Let's start with a basic overview of cardinality and modality so that it becomes easier to understand how they are different from each other.
What is Cardinality?
Cardinality describes the maximum number of data objects that can participate in a relationship. In databases, cardinality is defined as the uniqueness of data values that are contained in a column.
High cardinality means the column contains a large percentage of totally unique values. On the other hand, low cardinality means the column has a lot of "repeats" in its data range. Cardinality between the tables can be classified into different types such as one−to−one, many−to−one or many−to−many.
What is Modality?
Modality is absolutely different from cardinality because −
The value of modality is computed as "0", if the relationship is optional or if there is no need for the relationship to occur.
If there is a necessity of the occurrence of a relationship, then the value of the modality is computed as "1".
Therefore, modality describes whether a relationship between two or more entities is needed or not. Thus, in the case of modality, the modality can be classified into two types namely nullable modality and non−nullable modality.
Difference between Cardinality and Modality
The following table highlights the important differences between Cardinality and Modality −
| Cardinality | Modality |
|---|---|
| It tells about the maximum number of associations between rows of tables. | It tells about the minimum number of row associations in a table. |
| There are different types − One−to−one, one−to−many, many−to−many. | There are different types − Nullable and Not nullable. |
| Oneto one is where the occurrence of object 'A' can relate to one and only one occurrence of object 'B', and vice−versa. | Nullable columns accept an empty field. |
| Onetomany is where the occurrence of object 'A' can relate to multiple occurrences of object 'B', but object 'B' can relate to a single occurrence of object 'A'. | The non−nullable column doesn't accept null values. |
| Manytomany is where multiple occurrences of object 'A' can relate to multiple occurrences of object 'B', and vice−versa. | Modality states the possibility of making relationships among data objects. |
Conclusion
Cardinality and Modality are important concepts in databases. The most significant difference between cardinality and modality is that cardinality represents the maximum number of data objects that can participate in a relationship, whereas modality represents the probability of making relationships among data objects.
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