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Can anyone please explain in clear words what is generally meant by "modality of data"? I know what modality means with respect to distributions.

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One definition for "modality of data" is how many different types of data are included in the dataset.

For example: Images along with tags and text.

Different modalities usually have very different statistical properties, which can make the dataset more complex to work with.

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Cardinality and Modality are the two data modelling concepts used for understanding the information domain of the problem. For analysing the data objects, data attributes and relationships structures, the terms given above are very important.

The major difference between cardinality and modality is that, the cardinality is defined as the metric used to specify the number of occurrences of one object related to the number of occurrences of another object. On the contrary, modality signifies whether a certain data object must participate in the relationship or not.

Definition of Modality The Modality is completely different from the cardinality. Its value is computed as “o” when there is no requirement for the relationship to occur or if the relationship is optional. The modality value is “1” if there is a compulsion for the occurrence of a relationship. In simple words, it describes whether a relationship between two or more entities is even required or not.

Let’s take an example of a PAN card and its related debit cardholders. In the Debit card holder table, there will be a PAN card number, which makes a link to the PAN card holder as a bank account holder necessarily required to have a PAN card. Now, if the modality is in this example is “0” then there present a row without PAN card number but if it is “1” then we should have a value in the PAN card number.

So, here if the modality is “0” or more then “0” which specifies the Debit cardholder does not have any PAN card number hence is not needed to be held. Debit card holder table not only maintains the active cardholder data but also the data of users which have closed their bank accounts and this is called NULLABLE column due to its acceptance of an empty field.

When the modality is 1, the debit cardholder must be having a PAN card number, which means a bank account with no PAN card number cannot be included in the table. Therefore this column is considered to be NOT NULL column as it does not accept null values

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