3 ms·

> it's not about formal definitions. It's about whether you're conceptually putting multiple pieces of data into a single field. Which has everything to do with

by goto11 5y ago

> it's not about formal definitions. It's about whether you're conceptually putting multiple pieces of data into a single field. Which has everything to do with first normal form. I'm really confused by this argument. It seems to you suggest "first normal form" does not just cover the formal definition (eliminate nested relations) but also a general guideline to avoid putting "multiple pieces of data into a single field". While the second part is certainly a very reasonable design guideline, it is a completely different thing than 1NF, and conflating these two things will IMHO just lead to a muddy understanding of both. The guideline to avoid conceptually putting multiple pieces of data into a single field cannot have a formal definition, since it depends on business requirements what constitute a piece of data. For example a phone number has multiple segments like country code, area code, line code etc depending on country. Should a phone number be treated as one piece of data or multiple pieces of data? Depends on what you need to do with the phone number. 2NF is defined to encompass 1NF, i.e. in order to be in 2NF a relation has to be an 1NF (indeed this is the case for all the higher normal forms). But if we confuse 1NF with some vague guideline without objective criteria, there is no way to determine if a relation is in 2NF either. This undermines the whole notion of normal forms.

CRConrad 5y ago
> The guideline to avoid conceptually putting multiple pieces of data into a single field cannot have a formal definition, since it depends on business requirements what constitute a piece of data. For example a phone number has multiple segments like country code, area code, line code etc depending on country. Should a phone number be treated as one piece of data or multiple pieces of data? Depends on what you need to do with the phone number. A phone number is what you dial to call someone; it's the value you need to use a telephone, which is what telephone numbers are for. A comma-delimited list of telephone numbers isn't. > According to Date's definition, a table is in first normal form if and only if it is "isomorphic to some relation", which means, specifically, that it satisfies the following five conditions: > ... > 4. Every row-and-column intersection contains exactly one value from the applicable domain (and nothing else). -- https://en.wikipedia.org/wiki/Database_normalization https://en.wikipedia.org/wiki/Database_normalization , quoting Date, C. J. (2007). What First Normal Form Really Means. Date on Database: Writings 2000–2006. Apress. pp. 127–128. ISBN 978-1-4842-2029-0. Surely "exactly one value" from the applicable domain of telephone numbers is a telephone number, not a comma-delimited list of telephone numbers.
- goto11 5y ago
  > Surely "exactly one value" from the applicable domain of telephone numbers is a telephone number, not a comma-delimited list of telephone numbers. Yes certainly. But note that when we talk about comma-separated values, we are talking about multiple values encoded into a string and treated as a single string (or VARCHAR) value on the database level. In other words, the domain is the set of strings, not the set of phone numbers. If a database has a phone number type, it can use that as domain and ensure that an attribute can only contain a single phone number.
  - CRConrad 5y ago
    And an RDBMS on-disk structure is just a binary blob, so let's have those as values within another RDBMS... No, that's still a whole fricking database. Just because it's encoded into a single binary blob doesn't change that. Neither does encoding a list of telephone numbers into a string change the fact that it's a list.
    - goto11 5y ago
      1NF is defined in terms of attribute domains on the logical model. It all comes down to if the value is atomic with regard to relational algebra. Can you project attributes or insert tuples in the value using the standard relational operators? Then it is a relation, and you have a 1NF violation.

by goto11 5y ago

CRConrad 5y ago

> The guideline to avoid conceptually putting multiple pieces of data into a single field cannot have a formal definition, since it depends on business requirements what constitute a piece of data. For example a phone number has multiple segments like country code, area code, line code etc depending on country. Should a phone number be treated as one piece of data or multiple pieces of data? Depends on what you need to do with the phone number. A phone number is what you dial to call someone; it's the value you need to use a telephone, which is what telephone numbers are for. A comma-delimited list of telephone numbers isn't. > According to Date's definition, a table is in first normal form if and only if it is "isomorphic to some relation", which means, specifically, that it satisfies the following five conditions: > ... > 4. Every row-and-column intersection contains exactly one value from the applicable domain (and nothing else). -- https://en.wikipedia.org/wiki/Database_normalization https://en.wikipedia.org/wiki/Database_normalization , quoting Date, C. J. (2007). What First Normal Form Really Means. Date on Database: Writings 2000–2006. Apress. pp. 127–128. ISBN 978-1-4842-2029-0. Surely "exactly one value" from the applicable domain of telephone numbers is a telephone number, not a comma-delimited list of telephone numbers.

goto11 5y ago
> Surely "exactly one value" from the applicable domain of telephone numbers is a telephone number, not a comma-delimited list of telephone numbers. Yes certainly. But note that when we talk about comma-separated values, we are talking about multiple values encoded into a string and treated as a single string (or VARCHAR) value on the database level. In other words, the domain is the set of strings, not the set of phone numbers. If a database has a phone number type, it can use that as domain and ensure that an attribute can only contain a single phone number.
- CRConrad 5y ago
  And an RDBMS on-disk structure is just a binary blob, so let's have those as values within another RDBMS... No, that's still a whole fricking database. Just because it's encoded into a single binary blob doesn't change that. Neither does encoding a list of telephone numbers into a string change the fact that it's a list.
  - goto11 5y ago
    1NF is defined in terms of attribute domains on the logical model. It all comes down to if the value is atomic with regard to relational algebra. Can you project attributes or insert tuples in the value using the standard relational operators? Then it is a relation, and you have a 1NF violation.