ExpressionScript Engine – Hitri vodnik
From LimeSurvey Manual
Vodnik za hiter začetek
Znotraj LimeSurvey lahko dodatno prilagodite svoje ankete z uporabo ExpressionScript (kratko: ES). Stranska opomba: "ExpressionScript je bil v prejšnji različici imenovan Expression Manager (EM). Če ste kje prebrali Expression Manager, je to samo staro ime ES."
ES se lahko uporablja za določitev naslednjega:
- Navigacija/Razvejanje - omogoča anketirančevim odgovorom, da spremenijo vrstni red, v katerem so prikazana vprašanja;
- Prilagoditev/Cevovod' - vam pomaga ubesediti vprašanje (kot se nanaša na predhodni odgovori ali spreganje stavkov glede na starost ali spol vaših predmetov) ali kako ustvariti poročila po meri (kot so rezultati ocenjevanja ali prilagojeni nasveti);
- Validacija - zagotavlja, da odgovori prestanejo določena merila, kot so najmanjše in največje vrednosti ali določen vnosni vzorec.
ES ponuja intuitiven način za določanje logike za vsako od teh funkcij. Skoraj vse, kar lahko zapišete kot standardno matematično enačbo, je veljaven izraz.
ES trenutno omogoča dostop do 70 funkcij in ga je mogoče enostavno razširiti, da podpira več. Prav tako vam omogoča dostop do spremenljivk
z uporabo človeku berljivih imen spremenljivk (namesto SGQA names).
Prihajajoči razdelki prikazujejo glavna mesta, kjer se uporablja ES.
Nekatere ankete uporabljajo "Goto Logic", tako da če na vprašanje 1 odgovorite z možnostjo C, ste preusmerjeni na vprašanje 5. Ta pristop je zelo omejen, saj ga je težko potrditi. Poleg tega se zlahka pokvari, ko morate preurediti vprašanja. Po drugi strani pa ES uporablja Boolove relevantne enačbe za določitev vseh pogojev, pod katerimi bi lahko bilo vprašanje veljavno. Če je vprašanje relevantno, je vprašanje prikazano, v nasprotnem primeru ni uporabno in vrednost "NULL" je shranjena v bazi podatkov.
Da bi bolje razumeli koncept ustreznosti, se osredotočimo na naslednjo raziskavo, ki izračuna indeks telesne mase (ITM) anketirancev. Če ga želite prenesti, kliknite na naslednjo povezavo: Primer raziskave indeksa telesne mase.
Enačba ustreznosti je prikazana spodaj v stolpcu Relevantnost za imenom spremenljivke. Vrednosti ustreznosti teže, teže_enot, višine in višine so vse 1 (privzeta vrednost), kar pomeni, da so ta vprašanja vedno prikazana. Vendar pa je relevantnost za ITM {!is_empty(height) in !is_empty(weight)}, kar pomeni, da bo ITM izračunan samo, če subjekt vnese vrednost tako za višino kot za težo (s čimer se izognemo tveganju, da bi dobili napako nič). Tudi vprašanje "Poročilo" je prikazano le, če anketiranec odgovori na vsa štiri glavna vprašanja (višina, enote višine, teža, enote teže).
Ustreznost je prikazana in jo je mogoče urejati, ko:
- želite videti/urediti ustreznost na ravni vprašanja
- želite si ogledati/urediti ustreznost na ravni skupine
Ogled/urejanje Ustreznost na ravni vprašanja
Ta enačba izračuna indeks telesne mase (ITM). Vpraša se le, ali oseba vnese svojo višino in težo.
To je zaslon za urejanje vprašanja "BMI".
Upoštevajte, da ne uporabite zavitih oklepajev, ko vnesete enačbo ustreznosti.
Ogled/urejanje ustreznosti na ravni skupine
Osredotočimo se zdaj na drug primer – preprosto popisno raziskavo. Če ga želite prenesti, kliknite naslednjo povezavo: Primer popisne raziskave.
Prva stran vpraša, koliko ljudi živi z vami, in to shrani v spremenljivko "cohabs". Ta stran je prikazana samo, če imate več kot enega sostanovalca (prikazana je za drugo osebo, ki živi z vami). Tudi p2name, p2age. p2sum se prikažejo le, če vprašanje pred vsakim od njih vsebuje odgovor.
So, the group also has question-level relevance criteria, such that some questions only appear if you answered certain questions before them (e.g., p2age is displayed if p2name was answered). ES combines the Group and Question-level relevance for you. Questions in a group are only asked if the group as a whole is relevant. Then, only the subset of questions within the group that are relevant are asked.
Here is the screenshot for editing the group-level relevance of Cohabitant 2:
Note that you do not use the curly braces when you enter a relevance equation.
Tailoring/Piping
ES lets you easily do simple and complex conditional tailoring. Sometimes you just need a simple substitution, like saying, "You said you purchased [Product]. What did you like best about it?". Sometimes you need conditional substitution like "[Mr./Mrs.] [LastName], would you be willing to complete our survey?". In this case, you want to use "Mr. or Mrs." based on the person's gender. Other times you need even more complex substitution (such as based upon a mathematical computation). ES supports each of these types of tailoring/piping.
Conditional Equations
The Body Mass Index example shows the ability to compute a person's BMI, even while letting them enter their height and weight in two different units (cms vs inches and kgs vs lbs):
In this case, weightkg is {if(weightunits == "kg", weight, weight * 0.453592)}. This "if()" function means that if the subject enters the weight using kilograms, use that value, otherwise multiply the entered value (pounds is the alternative) by 0.453592 to convert it to kilograms. The heightm variable uses a similar approach to compute the person's height in meters (height in cms/100), even if he has entered his height in inches (1 meter=3.28084 inches).
BMI is computed as: {weightkg / (heightm * heightm)}.
Lastly, the report conditionally tailors the message for the subject, telling her what he entered. (e.g., "You said you are 2 meters tall and weight 70 kg.")
In the below image, weightstatus uses nested "if()" statements to categorize the person as underweight to severely obese. You can see its equation by checking its logic:
From the edit window for this question, you can see two things:
- Tailoring must surround expressions with curly braces
- Expressions can span multiple lines if, as in this case, you want to make it easier to read the nested conditional logic.
Tailored Questions, Answers, and Reports
Note: Dynamic tailoring may not work if answer options are made available in select boxes on the same question page. This results from the fact that tailoring inserts a <span> tag which is not valid inside select options.The BMI report looks like this:
Here is the edit window for the same question.
Anything within curly braces is treated as an expression, being syntax-highlighted (color coded) in the prior image. If you have any typos (such as misspelled or undefined variable names or functions), ES would show an error. In our below example:
- heightunit.shown is an undefined variable name (it is actually heightunits.shown) and
- "rnd()" is an undefined function (the proper function name is "round()").
In both cases, the errors are located within a red box to make it easier to spot and fix them.
You can also see that you can quickly create complex reports, such as a table of entered values or tailored advice.
Please remember that all tailoring must surround expressions with curly braces so that LimeSurvey knows which parts of the question are free text and which should be parsed by the ExpressionScript engine.
Validation
ES controls how most of the advanced question options work. These control aspects like min/max numbers of answers, min/max individual values, min/max sum values, and checking that entered values match specified string patterns. Any value in one of those fields is considered an expression, so you can have min/max criteria with complex conditional relationships to other questions.
In all of these cases, since the advanced question attribute is always considered an expression, you do not use curly braces when specifying it.
The sample surveys page shows many working examples containing a variety of validation expressions.
ExpressionScript - presentation
To find out more about ExpressionScript and how you can use different expressions to enhance your survey, please click on the following link.