diff --git a/app/AccountClass.php b/app/AccountClass.php
index 1aca5a3..18edca4 100644
--- a/app/AccountClass.php
+++ b/app/AccountClass.php
@@ -6,5 +6,13 @@ use Illuminate\Database\Eloquent\Model;
 
 class AccountClass extends Model
 {
-    //
+    /*
+     * Get the IO-type of the account class.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function ioType()
+    {
+        return $this->belongsTo('App\IOType');
+    }
 }
diff --git a/app/AccountType.php b/app/AccountType.php
index 40238ca..cb3f05e 100644
--- a/app/AccountType.php
+++ b/app/AccountType.php
@@ -6,5 +6,23 @@ use Illuminate\Database\Eloquent\Model;
 
 class AccountType extends Model
 {
-    //
+    /*
+     * Get the account class of the account type.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function accountClass()
+    {
+        return $this->belongsTo('App\AccountClass');
+    }
+    
+    /*
+     * Get the IO-type of the account type.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function ioType()
+    {
+        return $this->accountClass->ioType();
+    }
 }
diff --git a/app/Booking.php b/app/Booking.php
index 663e86c..04013cd 100644
--- a/app/Booking.php
+++ b/app/Booking.php
@@ -6,5 +6,13 @@ use Illuminate\Database\Eloquent\Model;
 
 class Booking extends Model
 {
-    //
+    public function amount()
+    {
+        return $this->hasMany('App\SubBooking')->amount;
+    }
+
+    public function signedAmount()
+    {
+        return $this->amount;
+    }
 }
diff --git a/app/PersonTarget.php b/app/PersonTarget.php
index aa47ae4..1ae83b8 100644
--- a/app/PersonTarget.php
+++ b/app/PersonTarget.php
@@ -6,13 +6,76 @@ use Illuminate\Database\Eloquent\Model;
 
 class PersonTarget extends Model
 {
+    /*
+     * Get the signed amount of the target.
+     *
+     * @return float
+     */
+    public function signedAmount()
+    {
+        return $this->amount * $this->ioType->factor;
+    }
+
+    /**************************************************************************
+     * BOOKINGS                                                               *
+     **************************************************************************/
+    
     /*
      * Get all bookings associated with a target.
      *
      * @return Illuminate\Database\Eloquent\Collection
      */
-    public function getBookings()
+    public function bookings()
     {
-        return $this->hasMany('\App\SubBooking')->get();
+        return $this->hasMany('\App\SubBooking');
+    }
+    
+    /**************************************************************************
+     * IOTYPES                                                                *
+     **************************************************************************/
+
+    /*
+     * Get the IOType of the target.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function ioType()
+    {
+        return $this->belongsTo('App\IOType');
+    }
+
+    /**************************************************************************
+     * ACTUALS                                                                *
+     **************************************************************************/
+    
+    /*
+     * Get the actuals connected with the target.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\HasMany
+     */
+    public function actuals()
+    {
+        return $this->hasMany('App\SubBooking');
+    }
+
+    /*
+     * Return the sum of all actuals belonging to this target
+     *
+     * @return float 
+     */
+    public function actualsSum() {
+        return $this->actuals->each(function ($item, $key) {
+            $item['signedAmount'] = $item->signedAmount();
+        })->sum('signedAmount');
+    }
+
+    /*
+     * Get the difference of target and actually payed amount so far. I. e.
+     * return the amount still to be payed.
+     *
+     * @return float
+     */
+    public function difference() {
+        return $this->actualsSum() + $this->signedAmount();
     }
 }
diff --git a/app/SubBooking.php b/app/SubBooking.php
index 041f69f..ee87c88 100644
--- a/app/SubBooking.php
+++ b/app/SubBooking.php
@@ -6,13 +6,78 @@ use Illuminate\Database\Eloquent\Model;
 
 class SubBooking extends Model
 {
-     /*
-      * Get the booking date for a sub-booking.
-      *
-      * @return string
-      */
-     public function date()
-     {
-         return $this->belongsTo('\App\Booking', 'booking_id')->first()->date;
-     }
+    /**************************************************************************
+     * BOOKINGS                                                               *
+     **************************************************************************/
+
+    /*
+     * Get the booking which contains the sub-booking.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function booking() {
+        return $this->belongsTo('\App\Booking', 'booking_id');
+    }
+
+    /*
+     * Get the booking date for a sub-booking.
+     *
+     * @return string
+     */
+    public function date()
+    {
+        return $this->booking->date;
+    }
+    
+    /**************************************************************************
+     * ACCOUNT TYPES                                                          *
+     **************************************************************************/
+    
+    /*
+     * Get the account type related to the sub-booking. 
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function accountType() 
+    {
+        return $this->belongsTo('App\AccountType', 'account_type_id');
+    }
+
+    /*
+     * Get the IO-type of the sub-booking.
+     *
+     * @return 
+     */
+    public function ioType()
+    {
+        return $this->accountType->ioType();
+    }
+
+    /**************************************************************************
+     * PERSON TARGETS                                                         *
+     **************************************************************************/
+    
+    /*
+     * Get the person-target related to the sub-booking. 
+     *
+     * @return Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function personTarget()
+    {
+        return $this->belongsTo('App\PersonTarget', 'person_target_id');
+    }
+
+    /**************************************************************************
+     * PROJECTS                                                               *
+     **************************************************************************/
+    
+    /*
+     * Get the project related to the sub-booking.
+     *
+     * @return Illuminate\Database\Eloquent\Relations\belongsTo
+     */
+    public function project()
+    {
+        return $this->belongsTo('App\Project', 'project_id');
+    }
 }