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*Subject*: **RE: [office-formula] Formula Processing Model**

*From*:**"Dennis E. Hamilton" <dennis.hamilton@acm.org>***To*: "'Patrick Durusau'" <patrick@durusau.net>,<office-formula@lists.oasis-open.org>*Date*: Fri, 22 Jan 2010 10:21:12 -0800

I happen to believe that we do need a processing model for a number of reasons. One of them has to do with interdependent formulas in a (re-)calculation and the ways that data not provided directly in the formula itself is acquired. One might not be able to answer all of the questions, but a processing model of some sort is needed so one can tell at least what the questions are and which ones are not being answered (or, preferably. are explicitly and identifiably implementation-defined/-dependent). The interesting question is, what is the least one must constrain OpenFormula with normative language in order to have any prospect of interoperability without compelling out-of-band agreements among implementers (including use of a common code base) because the specification is inadequate on the subject. - Dennis MORE ANALYSIS AND THOUGHTS The interdependence with recalculation will arise, in the evaluator, when a cell or other value source referenced in the first formula is accessed and that source is determined by a formula. Clearly, if there is no known value, there will be a (re-) calculation. If there is a value that has been previously calculated, it is tricky whether recalculation should occur or not. Clearly recalculation is not required if the result would not be impacted. Presumably, recalculation will be done if the "recalculate" flag, the extra "=", is present. Or maybe not: If that same formula is indirectly referenced more than once in evaluation of another formula, how many times does the recalculation happen? Unfortunately, we don't have a way of saying "don't recalculate this." We only have a way of saying "must recalculate." There is probably more that could be said on how even "must recalculate" is handled (as I just suggested) and what its value(s) is/(are) in these situations. There are complex interdependencies. For example, one can, in expanding a set of calculations and the calculated results they depend on, arrive at a dependency on a formula whose recalculation is in progress. Evaluators have ways of detecting such things and failing. It helps that formulas tend to be free of side effects although there are issues when a formula depends on the same formula-determined value in more than one way, and when there are dependencies on external dynamic variables, as when using random numbers, NOW(), some external data access or user input, etc. I recall evaluators that will iterate some number of times seeking a stable result. (I haven't checked lately to see if current products have such features and whether they are user controllable.) There is also interaction with processor setting on whether recalculation is done every time a formula is entered or a value that a formula depends on is altered. Delayed recalculation can be more useful when recalculation is costly, but trouble-shooting and failure detection becomes far more complex, as is the evaluator determining an order to perform the recalculations in so everything works out and unbearable repetition of the same calculations is avoided. I'm not sure many cyclic-dependency failures ever show up in produced formulas these days. When there is immediate calculation on entry or alteration of a formula in my simple-spreadsheet work, a cyclic dependency usually causes an interruption that an user must act on and it is not clear the offending formula (that is, the one that reveals the problem) is even allowed into the spreadsheet if the user fails to act and if failing to act is even an option. Note that if formula evaluations are not immediately attempted or their dependencies assessed when entered by an user, this detection can be delayed until a recalculate point and be awful for an user to then figure out. There are more cases, and I am not sure it is always possible to prevent cycles and other inter-formula dependency cases (for example, if a cell reference is determined dynamically via functions that effectively calculate references or indexes). Probably the worst case of delayed recalculation is on "save," especially when the user or the operating system is attempting to save and close the spreadsheet in a dangerous situation (imminent power failure is my nightmare case, something that plagues both laptop and desktop workers). I'm not sure whether the persisted document (assuming work is not lost) can be assured to be in a clean, "conformant" state under such conditions. -----Original Message----- From: Patrick Durusau [mailto:patrick@durusau.net] http://lists.oasis-open.org/archives/office-formula/201001/msg00056.html Sent: Friday, January 22, 2010 04:39 To: office-formula@lists.oasis-open.org Subject: Re: [office-formula] Formula Processing Model Eike, Eike Rathke wrote: http://lists.oasis-open.org/archives/office-formula/201001/msg00055.html > Hi Patrick, > > > <snip> http://lists.oasis-open.org/archives/office-formula/201001/msg00054.html >> So, the lead in paragraph under General: >> >> "OpenFormula defines the semantics of expressions, when recalcalculation >> occurs, and limits on formulas. It does not specify any particular >> process for evaluations consistent with those definitions." >> > > Actually we do not define when recalculation occurs, with the one > exception of formulas tagged for forced recalculation. It is up to the > implementation to decide when a formula or a part thereof is to be > recalculated. > > I was re-casting: "This section describes the basic formula processing model: how expressions are calculated, when recalculation occurs, and limits on formulas." But after re-reading the section on recalculation, it is just advisory and not normative. Yes? Do we need to reduce and keep as a note, perhaps with formulas tagged for forced recalculation? The opening line then becomes: "OpenFormula defines the semantics of expressions and limits on those expressions. It does not specify any particular process for evaluations consistent with those definitions." Thinking that saying "formulas" isn't any different from "expression." Yes? Hope you are looking forward to a great weekend! Patrick -- Patrick Durusau patrick@durusau.net Chair, V1 - US TAG to JTC 1/SC 34 Convener, JTC 1/SC 34/WG 3 (Topic Maps) Editor, OpenDocument Format TC (OASIS), Project Editor ISO/IEC 26300 Co-Editor, ISO/IEC 13250-1, 13250-5 (Topic Maps) --------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that generates this mail. Follow this link to all your TCs in OASIS at: https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php

**Follow-Ups**:**RE: [office-formula] Formula Processing Model***From:*robert_weir@us.ibm.com

**References**:**Formula Processing Model***From:*Patrick Durusau <patrick@durusau.net>

**Re: [office-formula] Formula Processing Model***From:*Eike Rathke <erack@sun.com>

**Re: [office-formula] Formula Processing Model***From:*Patrick Durusau <patrick@durusau.net>

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