title: Use Case Diagrams - Are arrows absolutely necessary?
body: <p>Is it absolutely necessary to use &quot;arrows&quot; to show association between an actor and a use case in a use case diagram?</p>
  <p>I recently had to draw one for my Software Engineering assignment. But after doing a bit of research online on many articles, papers, online books and lecture notes from numerous other universities, it seemed that majority of use case diagrams regardless of how much potential they have to show some kind of &quot;flow&quot; or &quot;navigability&quot;, have no arrows, while some examples have arrows.</p>
  <p>So I consulted my friend who is a final year student and has already studied what I have told me I shouldn't have arrows between my actor and use case and even his Requirements Engineering lecturer taught students not to use arrows. So I made a conscious decision not to use arrows and used solid lines instead to show my use case associations.</p>
  <p>Here is my diagram- <a href="http://i41.tinypic.com/2ccuo90.jpg" rel="nofollow noreferrer">click</a></p>
  <p>However, when I received the marks for my assignment, I was astonished to find out that I was given a zero for not using arrows. Even if it was mandatory to use them, there is an abundance of evidence that a solid line can be used for bi-directional association. So shouldn't I receive at least some marks for it?</p>
  <p>Obviously I asked for an explanation from my lecturer who I will see next week to discuss this point, but if she tells me I should have used arrows, what argument can I make against it? I would be grateful if someone can kindly give me good advice with appropriate references to some professional sources.</p>
  <p>Thank you very much for reading and I hope to read your response soon.</p>
  <hr />
  <p><strong>EDIT</strong></p>
  <p>Thank you guys. I really appreciate the answers you have given me. This whole confusion started because the only notation the lecturer provided was a single,very simple example of library use case diagram in one of the lecture notes, which had arrows. But it was not made very clear that it was the definitive notation. Another reason I didn't think it was mandatory is because when it came to explaining notations for drawing a data-flow diagram, she made it abundantly clear to using her specific notations, but it is not that uncommon for DFD's to have different notations in different sources, whereas I could find very little evidence to make the use of arrows in use-case diagrams necessary.</p>
  <p>That said, even before going through without arrows, I remember asking one of the tutors (not the lecturer) during a tutorial session what's the difference between having and arrowed line and a solid line and he said there is none and I could use both. Obviously for that I only have my word and from what you guys have said, I doubt anyone in an academic position would admit to telling something that could put them in a defensive position. My mistake was not speaking to the lecturer directly, but in hindsight I obviously would have done it.</p>
  <p>Anyway, I will speak to her regarding all this information and request her to take this &quot;honest mistake&quot; into consideration. It's also not just the use case diagram but a couple of other questions that I lost an unusual amount of marks on, especially when my answers are almost identical to the model answers she provided. I also know a lot of other students who have requested their assignments get remarked.</p>
  <p>Hopefully she will be kind and use good judgement to improve my mark. I will post back here when I find out.</p>
  <p>Thanks again for your help and please post any other info/suggestions you may have. :)</p>
  <hr />
  <p><strong>EDIT 2</strong></p>
  <p>Sorry guys, I have another question.</p>
  <p>Here is the scenario that was given in the assignment to draw the use case diagram.</p>
  <blockquote>
  <p>CONTHETICKET is a ticket agency
  dealing in Concert and Theatre
  tickets. <strong>Concert and theatre venues
  provide CONTHETICKET with a constant
  stream of information on forthcoming
  events</strong>, which is then used by the
  Manager to compile a fixture list for
  use by the sales staff in responding
  to customer calls. The manager selects
  some events for which CONTHETICKET
  will purchase a number of tickets in
  advance, thereby benefiting from
  discounts negotiated with the venues.</p>
  <p>He personally sends the orders for the
  tickets together with the agreed
  payments to the venues, and once
  tickets are received, he files them in
  the ticket File.</p>
  <p>When customers ring the sales team,
  their ticket requests are checked
  against the ticket file. If
  pre-purchased tickets are available
  they are put in an envelope marked
  with the customer's name and address,
  and filed in a provisional orders
  file. If not, the sales team fills out
  a ticket request form and put it in a
  tray for collection by the post clerk.</p>
  <p>The payments section checks the
  provisional orders file daily. They
  send an invoice to the customer and
  await payment. A copy of the invoice
  is kept on file. When a payment is
  received, the payments section match
  the payment with the appropriate
  invoice, and if satisfied place
  another copy of the invoice in a
  despatch file with instructions to
  despatch the tickets.</p>
  <p>The post clerks checks the despatch
  file each day and retrieves the
  appropriate tickets from the
  provisional orders file and sends them
  to the appropriate customers.</p>
  </blockquote>
  <p>As you can see from my <a href="http://i41.tinypic.com/2ccuo90.jpg" rel="nofollow noreferrer">diagram</a> I have an &quot;Concert &amp; Theatre Venues&quot; as an actor.</p>
  <p>From The Elements of UML 2.0 Style, Scott W. Ambler:</p>
  <p>&quot;An actor is a person, organization, or external system that plays a role in one or more interactions with your system (actors are typically drawn as stick figures on UML Use Case diagrams).&quot;</p>
  <p>However, on my marked assignment, the lecturer commented that it should not be an actor. Can you please tell me whether or not you think it should be an actor and why.</p>
  <p>My rationale behind it is CT&amp;V are supplying event information which is then used by the manager to order/file tickets, also supplied by CT&amp;V.</p>
  <p>Thank you very much.</p>