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hekate:attributes [2008/11/19 19:02] ligeza |
hekate:attributes [2019/06/27 15:49] (current) |
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| **Version**: Draft 2008Q3 | **Version**: Draft 2008Q3 | ||
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| + | //Please put bigger remarks/discussusion, to the [[hekatedev:attributes|attributes development page]]// | ||
| ===== Introduction ===== | ===== Introduction ===== | ||
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| Currently there are no plans to support regions algebra, that is to allow treating the value set as an ordord one (a list). | Currently there are no plans to support regions algebra, that is to allow treating the value set as an ordord one (a list). | ||
| - | ==== ND and NULL ==== | + | ==== NULL ==== |
| To provide the proper semantics: "no value", "unset", "not defined yet", etc. | To provide the proper semantics: "no value", "unset", "not defined yet", etc. | ||
| - | the special value //ND// (NOT_DEFINED) is introduced. | + | the special value //NULL// is introduced. |
| Following the RDBM convention and logic, a //NULL// attribute value is possible. | Following the RDBM convention and logic, a //NULL// attribute value is possible. | ||
| The semantics can be: "no value", "unset", "not defined yet", etc. | The semantics can be: "no value", "unset", "not defined yet", etc. | ||
| - | In his case this is simply //ND//. | + | Yes; to me, we should accept //NULL// exactly as it is in RDB systems. This allows to import data //as they are//. |
| - | However, we could consider //another// semantics, such as "unknown" | + | See here for the [[hekate:alsvfd#any_and_null|binding resolution]]. |
| + | |||
| + | However, we could consider //another// semantics, such as "unknown", see below. | ||
| + | |||
| + | ==== ND or NA ==== | ||
| + | On the other hand, we can consider introducing //ND// or //NA// as for example the capacity of and electric engine, | ||
| + | meaning "does not apply", e.g. "maiden name" in case of a male. | ||
| - | FIXME ALi | ||
| NULL as "unknown" should be treated as an extension. | NULL as "unknown" should be treated as an extension. | ||
| - | Its use should be explictly allowed in the attribute specification. | + | Its use should be explicitly allowed in the attribute specification. |
| - | Yes; to me, we should accept //NULL// exactly as it is in RDB systems. This allows to import data //as they are//. | ||
| - | On the other hand, we can consider introducing //ND// as for example the capacity of and electric engine. | ||
| ==== Explicit Notation ==== | ==== Explicit Notation ==== | ||
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| ==== Implicit Notation ==== | ==== Implicit Notation ==== | ||
| - | FIXME ALi | ||
| For setting attribute value the same implicit notation as for the domains should be used (a sum of ranges or values), | For setting attribute value the same implicit notation as for the domains should be used (a sum of ranges or values), | ||
| ''i.e. S=<5,8>u{3}.'' | ''i.e. S=<5,8>u{3}.'' | ||
| at both the HML and HMR levels. | at both the HML and HMR levels. | ||
| + | |||
| + | I agree. We should define the rules for well-formed expressions (enabling unique calculation of values), and allow for using it. This should be based on set algebra and incorporate the notational variants, such as ''A > 5'' (which in fact means ''A={6,7}'' if the domain of A is {1,2,3,4,5,6,7}. | ||
| + | |||
| + | So we use the //sum// SetTheory operator and sets of values. | ||
| + | |||
| + | Syntactic suger on the interface level, | ||
| + | consider attribute T, domain {0,50}, we mean, t=<10, the tool sould hint, t=<0,10>, | ||
| + | in //STATE// we store t=<0,10>, see above. | ||
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| //Symbol// might also be called //String//. | //Symbol// might also be called //String//. | ||
| + | |||
| + | check types in Hibernate!!! FIXME | ||
| Basic types in other languages (also called primitive types): | Basic types in other languages (also called primitive types): | ||
