--- title: "XPath validations,expressions, default values and checks...need help!" url: "https://openforis.support/questions/526/xpath-validationsexpressions-default-values-and-checksneed-help" tags: ["collect", "collectmobile"] status: "answered" score: 0 answer_count: 2 asked: "2016-05-11T20:24:25" last_activity: "2016-05-12T11:51:14" source: "Open Foris Support - Q&A Forum" license: "Copyright Open Foris, 2026. Some rights reserved under creative commons license." --- # XPath validations,expressions, default values and checks...need help! Asked by collector on 2016-05-11 Dear all, Working hard in the Collect Survey Designer ( found a v[ideo to design Collect Earth surveys in youtube][1] ) and I am trying to design a couple of new surveys. I have managed to get a few **XPath** validation expressions working but I must admit I am a bit lost... could anyone point me in the right direction of what should I learn, or what are kind of general XPath functions one can use??? **Validations, default values and the possibility to show/hide attributes** in the interface depending on other values is a strong feature, but documentation is weak... Thanks!! [1]: https://www.youtube.com/watch?v=j2ruGSzJg0Y ## Answer (score 2, by javier on 2016-05-12) Link: https://openforis.support/questions/526/xpath-validationsexpressions-default-values-and-checksneed-help/529 Hi...I have written a document with some XPath examples, based on two inheritance hierarchies among the entities: one more complex (cluster->plot) and one simpler (only plot). See below: Link to document : [HERE][1] **EXAMPLES OF CODE IN OPEN FORIS Collect** **General hierarchical structures (either cluster or plot-based)** Comparison checks (i.e., start_date, start_time, end_time, tree_no, azimuth, tree distance,dbh, total_height and bole_height): Example attribute (number type): Path: /plot/details/elevation Severity Error Message Elevation must be between 0 and 4000 m 0 <= elevation <= 4000 Example attribute (date type): Path: /cluster/start_date Severity Error Message You have written the starting date in the future! start_date <= idm:currentDate() Example attribute (time type): Path: /cluster/start_time Severity Warning Message Working hours for the survey should be from 06:00 to 19:00! 0600 < start_time <= 1900 Example attribute (time type): Path: /cluster/end_time Severity Error Message End time should be always after start time start_time <= end_time (Here we assume that start_time and end_time are under the same entity, i.e., cluster, or plot) Example attribute (number type): Path: /cluster/plot/tree/tree_no Severity Error Message tree number must be >0 0 < tree_no **Example attribute (number type): Path: /cluster/plot/tree/azimuth** Severity Error Message angle must be between 0 (inclusive) and 360 (exclusive) 0 <= azimuth < 360 **Example attribute (number type, refers to tree distance): Path: /cluster/plot/tree/distance** Severity Error Message tree distance must be positive 0 <= distance Severity Error Message tree outside of plot. Plot radius is 12 m. distance <= 12 **Example attribute (number type): Path: /cluster/plot/tree/dbh** Severity Warning Message Unusually large dbh dbh < 200 Severity Error Message dbh must be positive 0 <= dbh Severity Error Message tree must be at least 20 cm if distance>2 m 20 <= dbh Apply when distance>2 Severity Error Message tree must be at least 5 cm in any case 5 <= dbh **Example attribute (number type): Path: /cluster/plot/tree/total_height** Severity Warning Message Unusually tall tree total_height < 80 Severity Error Message Impossibly tall tree total_height < 150 Severity Error Message height must be positive 0 <= total_height **Example attribute (number type): Path: /cluster/plot/tree/bole_height** Severity Error Message bole height must be positive 0 <= bole_height Severity Error Message bole height must be less or equal than total height bole_height <= total_height **Default values (i.e., start_date, start_time and tree_no):** Example attribute (date type): Path: /cluster/start_date Calculated value expressions: Expression: idm:currentDate() **Example attribute (time type): Path: /cluster/start_time** Calculated value expressions: Expression: idm:currentTime() Example attribute (number type): Path: /plot/tree/tree_id **Calculated value expressions**: Expression: math:max(parent()/tree/tree_id) + 1 (it will automatically increase the number every time a new tree is recorded in the plot) Surveys with Plot as sampling unit or root entity and tree as sub-entity **Distance checks (i.e., plot position):** Example attribute: Path: /plot/details/position Severity Error Message You are more than 50 m from plot location Destination point idm:samplingPointCoordinate(parent()/plot_id) Max distance (m) 50 Severity Warning Message You are more than 20 m from plot location **Destination point** idm:samplingPointCoordinate( parent()/plot_id) Max distance (m) 20 **Autocompletion** (click Calculated in the General tab fot the variable) in optional variables from sample design file (i.e., province as a column after design point coordinates in the sampling_design imported file): Example attribute (text type): Path: /plot/details/province Calculated value expressions: Expression: idm:samplingPointData('province', parent()/plot_id) Requirednes of variable if expression is satisfied (i.e., tree_height only required every three third tree): Example attribute (text type): Path: /plot/tree/tree_height Required only when expression is verified: tree_id mod 3 = 0 **Surveys with Cluster as sampling unit or root entity and plot and tree as sub-entities** **Distance checks (i.e., plot position):** Example attribute: Path: /cluster/plot/details/position Severity Error Message You are more than 100 m from plot location Destination point idm:samplingPointCoordinate(parent()/parent()/cluster_no, parent()/plot_no) Max distance (m) 100 Severity Warning Message You are more than 20 m from plot location Destination point idm:samplingPointCoordinate(parent()/parent()/cluster_no, parent()/plot_no) Max distance (m) 20 **Autocompletion(click Calculated in the General tab fot the variable)** in optional variables from sample design file (i.e., province as a column after design point coordinates in the sampling_design imported file): Example attribute (text type): Path: /cluster/location/province Calculated value expressions: Expression: idm:samplingPointData('province', parent()/cluster_no) Example attribute (text type): Path: /cluster/plot/details/province Calculated value expressions: Expression: idm:samplingPointData('province', parent()/plot_no) Autocompletion (click Calculated in the General tab fot the variable) in tree-related variable (i.e., tree count): Example attribute (number type): Path: /cluster/plot/tree_count Calculated value expressions: Expression: math:max(parent()/plot/tree/tree_no) **Relevance of variable if expression is satisfied** (i.e., tree_count, plot position, and tree entity): Example attribute (number type): Path: /cluster/plot/tree_count Relevant only when expression is verified: parent()/plot/details/accessibility=0 Example attribute (coordinates type): Path: /cluster/plot/details/position Relevant only when expression is verified: accessibility=0 (here we don’t need a hierarchical path since position and accessibility belong to the same hierarchy, i.e: parent()/plot/details/position and parent()/plot/details/accessibility) Example entity (multiple table layout): Path: /cluster/plot/tree Relevant only when expression is verified: details/accessibility=0 [1]: https://www.dropbox.com/s/554wqn6o3ztm24h/EXAMPLES%20OF%20CODE%20IN%20OPEN%20FORIS%20Collect.docx?dl=0 ## Answer (score 1, by collectearth on 2016-05-11) Link: https://openforis.support/questions/526/xpath-validationsexpressions-default-values-and-checksneed-help/528 This is a common question, as the XPath is a language that can be a bit complex for non-programmers, but don't panic, it is really not that hard (and actually quite logical) You can start by looking into the Collect documentation here : [Open Foris Wiki : XPath documentation][1] [W3Schools also has some more in-depth tutorial in XPath][2] [1]: http://www.openforis.org/OFwiki/index.php/Inventory_Data_Metamodel [2]: http://www.w3schools.com/xsl/xpath_intro.asp