tag:blogger.com,1999:blog-6411920579549337139.post2356116936338656531..comments2023-03-19T03:04:17.239-07:00Comments on DATABASE DEBUNKINGS: Conventional Wisdom and True Relational FeaturesFabian Pascalhttp://www.blogger.com/profile/01346669716885494092noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-6411920579549337139.post-35731882729895193532017-12-12T15:47:30.496-08:002017-12-12T15:47:30.496-08:00BTW, the RDM is an INTERPRETED formal system. It&#...BTW, the RDM is an INTERPRETED formal system. It's ADAPTED set theory and FOPL -- which are purely abstract -- to make it applicable to the real world that databases represent (e.g., math relations do not have keys, domains are ordered, etc.) So you gotta be careful when you use purely math arguments for the RDM -- it is APPLIED, not pure theory.Fabian Pascalhttps://www.blogger.com/profile/01346669716885494092noreply@blogger.comtag:blogger.com,1999:blog-6411920579549337139.post-60961348617377192282017-12-12T13:23:12.256-08:002017-12-12T13:23:12.256-08:00>If you say that domains have types, then you a...>If you say that domains have types, then you are saying that sets (domains) have named set of values (types).<br /><br />Again, read more carefully: there is a difference between DATA TYPE and type. I am using the term in a 2nd sense, not in the 1st.<br /><br />>That is why, a data sublanguage must be based on values, types and variables too.<br /><br />If it is a CCL yes. There is a DATA LANGUAGE and has a FOPL-based RELATIONAL DATA SUB-LANGUAGE component that expresses only the DATA MGMT FUNCTIONS of the DBMS -- manipulation and integrity. The other DBMS functions are not expressed in the data sublanguage, but in the data language which is not limited to FOPL. Insofar as the sublanguage is concerned there are no variables, because then it is not a FOPL only relational language.<br /><br />For the formal exposition of Codd's RDM and its correct interpretation -- as distinct from the current "understanding" in the industry you will have to wait for David McGoveran's book.<br /><br /><br />A relational data sub-language implements data management functions and<br /><br />Fabian Pascalhttps://www.blogger.com/profile/01346669716885494092noreply@blogger.comtag:blogger.com,1999:blog-6411920579549337139.post-63120238733094987832017-12-12T12:45:00.829-08:002017-12-12T12:45:00.829-08:00In the RDM, a domain is nothing but a set on which...In the RDM, a domain is nothing but a set on which a relation is defined. It is a mathematical concept. Domains are not types, but do not have types either. If you say that domains have types, then you are saying that sets (domains) have named set of values (types).<br />A language (from a computational perspective) must be based on values, types and variables. That is why, a data sublanguage must be based on values, types and variables too. In particular, a relational-based data sublanguage it is based on relation values, relation types and relation variables (relvars).<br />The RDM is a mathematical representation ("relational view of data", as E. F. Codd wrote) of real-world facts. But we need to translated it into a computational representation.<br />What do you mean by "under the covers"? That is not a formal definition.Alain Pereira Toledohttps://www.blogger.com/profile/01752298806632569416noreply@blogger.comtag:blogger.com,1999:blog-6411920579549337139.post-18640328900333877322017-12-12T09:54:45.615-08:002017-12-12T09:54:45.615-08:00I suggest you re-read the post more carefully. It ...I suggest you re-read the post more carefully. It clearly says that:<br /><br />1. Domains HAVE types, but ARE NOT types. So domain values do have types.<br /><br />2. There are relvars UNDER THE COVERS, but there must not be EXPLICIT RELVAR SEMANTICS in the data language.<br /><br />Fabian Pascalhttps://www.blogger.com/profile/01346669716885494092noreply@blogger.comtag:blogger.com,1999:blog-6411920579549337139.post-79263731821627205432017-12-12T09:23:45.260-08:002017-12-12T09:23:45.260-08:00A value is an individual constant. They can be sca...A value is an individual constant. They can be scalar or nonscalar. A scalar value has no user-visible component parts. By definition, a value can't be updated. In the RDM, tuples and relations are nonscalar values (not scalar values).<br />Every value is of some type. A type is a named set of values, and can be either scalar or nonscalar. So, if there are tuple and relation values, then there are tuple types and relation types.<br />A variable is a holder for a representation of a value. Variables have a location in time and space and can be updated (the current value of a variable can be replaced by another value). Every variable is of some type at some moment in time. Again, if there are tuple values and relation values, then there are tuple variables and relation variables (relvars).Alain Pereira Toledohttps://www.blogger.com/profile/01752298806632569416noreply@blogger.comtag:blogger.com,1999:blog-6411920579549337139.post-19559082198449130432017-12-10T23:14:03.782-08:002017-12-10T23:14:03.782-08:00Thanks for your interest in Rel!
You can read mor...Thanks for your interest in Rel!<br /><br />You can read more or download it from https://reldb.orgAnonymoushttps://www.blogger.com/profile/08654311651743679264noreply@blogger.com