/**
 * @author Thomas Kleinke
 */
export interface Literature {

    quotation: string;
    zenonId?: string;
}


export module Literature {

    export function generateLabel(literature: Literature, getTranslation: (key: string) => string): string {

        return literature.quotation + (literature.zenonId
            ? ' ('
            + getTranslation('zenonId')
            + ': ' + literature.zenonId + ')'
            : '');
    }


    export function isValid(literature: Literature): boolean {

        return literature.quotation !== undefined && literature.quotation.length > 0;
    }
}
/**
 * @author Thomas Kleinke
 */
export interface Literature {

    quotation: string;
    zenonId?: string;
}


export module Literature {

    export function generateLabel(literature: Literature, getTranslation: (key: string) => string): string {

        return literature.quotation + (literature.zenonId
            ? ' ('
            + getTranslation('zenonId')
            + ': ' + literature.zenonId + ')'
            : '');
    }
}
--- 
+++ 
@@ -18,4 +18,10 @@
             + ': ' + literature.zenonId + ')'
             : '');
     }
+
+
+    export function isValid(literature: Literature): boolean {
+
+        return literature.quotation !== undefined && literature.quotation.length > 0;
+    }
 }
Add basic validation function for Literature
