diff --git a/doc/handshake_sequence_uml.uxf b/doc/handshake_sequence_uml.uxf
new file mode 100644
index 0000000..71dfe5e
--- /dev/null
+++ b/doc/handshake_sequence_uml.uxf
@@ -0,0 +1,501 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<diagram program="umlet" version="14.3.0">
+  <zoom_level>9</zoom_level>
+  <element>
+    <id>UMLActor</id>
+    <coordinates>
+      <x>72</x>
+      <y>540</y>
+      <w>54</w>
+      <h>99</h>
+    </coordinates>
+    <panel_attributes>Client1</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>2196</x>
+      <y>504</y>
+      <w>198</w>
+      <h>171</h>
+    </coordinates>
+    <panel_attributes>Database
+halign=center
+bg=orange
+--</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>351</x>
+      <y>513</y>
+      <w>90</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>Main</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>531</x>
+      <y>513</y>
+      <w>90</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>Startup
+bg=orange</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>702</x>
+      <y>513</y>
+      <w>90</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>Client
+bg=yellow</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>873</x>
+      <y>513</y>
+      <w>90</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>LocalDB
+bg=pink</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1548</x>
+      <y>522</y>
+      <w>189</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>LoginCredentialsProcessor
+bg=cyan</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1809</x>
+      <y>522</y>
+      <w>135</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>PersistenceManager
+bg=gray</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>396</x>
+      <y>729</y>
+      <w>189</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+start javaFX app</panel_attributes>
+    <additional_attributes>190.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>387</x>
+      <y>720</y>
+      <w>18</w>
+      <h>54</h>
+    </coordinates>
+    <panel_attributes/>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>387</x>
+      <y>621</y>
+      <w>27</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>567</x>
+      <y>621</y>
+      <w>27</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>738</x>
+      <y>621</y>
+      <w>27</w>
+      <h>216</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;220.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>909</x>
+      <y>621</y>
+      <w>27</w>
+      <h>153</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;150.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>567</x>
+      <y>720</y>
+      <w>18</w>
+      <h>396</h>
+    </coordinates>
+    <panel_attributes>bg=orange</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>738</x>
+      <y>819</y>
+      <w>18</w>
+      <h>558</h>
+    </coordinates>
+    <panel_attributes>bg=yellow</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>909</x>
+      <y>756</y>
+      <w>18</w>
+      <h>621</h>
+    </coordinates>
+    <panel_attributes>bg=pink</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>576</x>
+      <y>756</y>
+      <w>351</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+initialize</panel_attributes>
+    <additional_attributes>370.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1062</x>
+      <y>513</y>
+      <w>90</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>Receiver
+bg=red</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1098</x>
+      <y>621</y>
+      <w>27</w>
+      <h>270</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;280.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1098</x>
+      <y>873</y>
+      <w>18</w>
+      <h>504</h>
+    </coordinates>
+    <panel_attributes>bg=red</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>576</x>
+      <y>1071</y>
+      <w>180</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+init receivers
+layer=0</panel_attributes>
+    <additional_attributes>180.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>576</x>
+      <y>828</y>
+      <w>180</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+perform handshake</panel_attributes>
+    <additional_attributes>180.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>747</x>
+      <y>873</y>
+      <w>369</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+init handhake receivers
+layer=0</panel_attributes>
+    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>747</x>
+      <y>1071</y>
+      <w>369</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+init permanent receivers
+layer=0</panel_attributes>
+    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1638</x>
+      <y>630</y>
+      <w>27</w>
+      <h>306</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;320.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1638</x>
+      <y>918</y>
+      <w>18</w>
+      <h>558</h>
+    </coordinates>
+    <panel_attributes>bg=cyan</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>747</x>
+      <y>918</y>
+      <w>909</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+send login credentials
+layer=0</panel_attributes>
+    <additional_attributes>990.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1872</x>
+      <y>630</y>
+      <w>27</w>
+      <h>306</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;320.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>1872</x>
+      <y>918</y>
+      <w>18</w>
+      <h>558</h>
+    </coordinates>
+    <panel_attributes>bg=gray</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1881</x>
+      <y>918</y>
+      <w>423</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+use queries
+layer=0</panel_attributes>
+    <additional_attributes>450.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>2286</x>
+      <y>666</y>
+      <w>27</w>
+      <h>270</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;280.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>2286</x>
+      <y>918</y>
+      <w>18</w>
+      <h>558</h>
+    </coordinates>
+    <panel_attributes>bg=orange</panel_attributes>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1647</x>
+      <y>918</y>
+      <w>243</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=&lt;&lt;-
+aquire data
+layer=0</panel_attributes>
+    <additional_attributes>250.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1881</x>
+      <y>954</y>
+      <w>423</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;&gt;
+send query responses
+layer=0</panel_attributes>
+    <additional_attributes>450.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1647</x>
+      <y>954</y>
+      <w>243</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;&gt;
+send aquired data
+layer=0</panel_attributes>
+    <additional_attributes>250.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>1107</x>
+      <y>990</y>
+      <w>549</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;&gt;
+send user, chats, pending messages, etc.
+layer=0</panel_attributes>
+    <additional_attributes>590.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>918</x>
+      <y>990</y>
+      <w>198</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;&gt;
+store data
+layer=0</panel_attributes>
+    <additional_attributes>200.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>99</x>
+      <y>729</y>
+      <w>306</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;
+start app</panel_attributes>
+    <additional_attributes>10.0;20.0;320.0;20.0</additional_attributes>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>90</x>
+      <y>621</y>
+      <w>27</w>
+      <h>117</h>
+    </coordinates>
+    <panel_attributes>lt=.</panel_attributes>
+    <additional_attributes>10.0;10.0;10.0;110.0</additional_attributes>
+  </element>
+  <element>
+    <id>UMLGeneric</id>
+    <coordinates>
+      <x>90</x>
+      <y>720</y>
+      <w>18</w>
+      <h>54</h>
+    </coordinates>
+    <panel_attributes/>
+    <additional_attributes/>
+  </element>
+  <element>
+    <id>Relation</id>
+    <coordinates>
+      <x>747</x>
+      <y>1026</y>
+      <w>369</w>
+      <h>36</h>
+    </coordinates>
+    <panel_attributes>lt=-&gt;&gt;
+online
+layer=0</panel_attributes>
+    <additional_attributes>390.0;20.0;10.0;20.0</additional_attributes>
+  </element>
+</diagram>