diff --git a/src/app/sample/sample.component.ts b/src/app/sample/sample.component.ts
index cfac79e..cdcfa03 100644
--- a/src/app/sample/sample.component.ts
+++ b/src/app/sample/sample.component.ts
@@ -239,12 +239,12 @@ export class SampleComponent implements OnInit, AfterContentChecked {
       this.samples.forEach((gSample, gIndex) => {
         if (this.d.id.conditionTemplates[gSample.condition.condition_template]) {
           this.d.id.conditionTemplates[gSample.condition.condition_template].parameters.forEach((parameter, pIndex) => {
-            this.attachValidator(this.cmForm, `conditionParameter-${gIndex}-${pIndex}`, parameter.range, true);
+            this.attachValidator(this.cmForm, `conditionParameter-${gIndex}-${pIndex}`, parameter.range);
           });
         }
         gSample.measurements.forEach((measurement, mIndex) => {
           this.d.id.measurementTemplates[measurement.measurement_template].parameters.forEach((parameter, pIndex) => {
-            this.attachValidator(this.cmForm, `measurementParameter-${gIndex}-${mIndex}-${pIndex}`, parameter.range, false);
+            this.attachValidator(this.cmForm, `measurementParameter-${gIndex}-${mIndex}-${pIndex}`, parameter.range);
           });
         });
       });
@@ -252,7 +252,7 @@ export class SampleComponent implements OnInit, AfterContentChecked {
 
     if (this.sampleForm && this.material.properties.material_template) {  // material template is set
       this.d.id.materialTemplates[this.material.properties.material_template].parameters.forEach((parameter, i) => {
-        this.attachValidator(this.sampleForm, 'materialParameter' + i, parameter.range, true);
+        this.attachValidator(this.sampleForm, 'materialParameter' + i, parameter.range);
       });
     }
 
@@ -288,10 +288,10 @@ export class SampleComponent implements OnInit, AfterContentChecked {
   }
 
   // attach validators specified in range to input with name
-  attachValidator(form, name: string, range: {[prop: string]: any}, required: boolean) {
+  attachValidator(form, name: string, range: {[prop: string]: any}) {
     if (form && form.form.get(name)) {
       const validators = [];
-      if (required) {
+      if (range.hasOwnProperty('required')) {
         validators.push(Validators.required);
       }
       if (range.hasOwnProperty('values')) {
diff --git a/src/app/services/validation.service.ts b/src/app/services/validation.service.ts
index 0deb86e..8584154 100644
--- a/src/app/services/validation.service.ts
+++ b/src/app/services/validation.service.ts
@@ -153,13 +153,12 @@ export class ValidationService {
           max: Joi.number(),
 
           type: Joi.string()
-            .valid('array')
+            .valid('string', 'number', 'boolean', 'array'),
+
+          required: Joi.boolean()
         })
           .oxor('values', 'min')
           .oxor('values', 'max')
-          .oxor('type', 'values')
-          .oxor('type', 'min')
-          .oxor('type', 'max')
           .required()
           .validate(JSON.parse(data));
         if (error) {