tailieunhanh - Managing time in relational databases- P22

Tham khảo tài liệu 'managing time in relational databases- p22', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 408 THE ASSERTED VERSIONING GLOSSARY Glossary Entries include See also Allen relationship fills . assert cognates Mechanics the cognate terms accept agree assent believe claim know say and think . Semantics terms which for purposes of the discussions in this book may be taken as synonymous with assert as that word is defined in this book. Comments There are important differences among these terms in the fields of epistemology and semantics. For example some terms designate what philosophers call speech acts while others designate what philosophers call propositional attitudes . 12 31 9999 Mechanics the latest date which can be represented by the SQL Server DBMS. Semantics a value for an end date which means that the end of the time period it delimits is unknown but assumed to be later than Now . Comments For other DBMSs the value used should similarly be the latest date which can be represented by that DBMS. Components end date Now time period. 9999 Mechanics a DBMS-agnostic representation of the latest date which can be represented by a specific DBMS. Semantics a DBMS-agnostic representation of a value for an end date which means that the end of the time period it delimits is unknown but assumed to be later than Now . Components end date Now time period. actionable Description data which is good enough for its intended purposes. Comments As a kind of shorthand we say that the assertion time period of a row is the period of time during which we assert that it is true. And if we discover that a row is incorrect and does not make a true statement we do end its assertion time period. But some true statements are not actionable. For example a currently effective row in a 100-column table may have 10 of its columns filled with accurate data and the other 90 columns empty. So that row makes a true statement as far as it goes but because it is so incomplete it is probably not a statement that provides enough information to act on. And some actionable statements are not .

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