<div dir="ltr">Ναι γινεται ετσι ειναι και στις διαφανειες. Αλλιως ειμαι ιδιαιτερα περιεργος να δω πως καποιος αντιμετωπιζει το γεγονος οτι ο εποπτης πρεπει να ειναι οντοτητα και οτι τα φαρμακεια εχουν 1 συμβολαιο το πολυ προς καθε  εταιρια.Σε μια τριπλη σχεση απο οτι εχω καταλαβει η πληθυκοτητα εκφραζεται περνωντας καθε οντοτητα σε συνδυασμο με τι γινομενο των αλλων 2 .Αρα δεν γινεται να εκφραστει το παραπανω ετσι με οποιονδηποτε συνδυασμο απο πληθυκοτητες.Μου διαφευγει κατι?   </div><div class="gmail_extra"><br><div class="gmail_quote">Στις 5 Νοεμβρίου 2016 - 9:42 μ.μ., ο χρήστης Παναγιώτης Καραμπάσης <span dir="ltr">&lt;<a href="mailto:viable.prefix@gmail.com" target="_blank">viable.prefix@gmail.com</a>&gt;</span> έγραψε:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Καλησπέρα,<br></div><div><br>Θα ήθελα να παραπέμψω στην ενότητα 7.8.5 Aggregation του βιβλίου του μαθήματος Database System Concepts, Silberschatz, Korth, Sudershan, 6th Edition.<br><br></div><div><i>Aggregation is an abstraction through which relationships are treated as higher-level entities. [...] Such an entity set is treated in the same manner as any other entity set.</i><br></div><div><br>Είναι κάτι που χρησιμοποίησα στο μοντέλο μου, ελπίζω να μην απαγορευτεί για κάποιο λόγο.<br><br></div>Ευχαριστώ.<br></div><div class="HOEnZb"><div class="h5"><br><div class="gmail_quote"><div dir="ltr">Στις Σάβ, 5 Νοε 2016 στις 9:27 μ.μ., ο/η Theodora Galani &lt;<a href="mailto:theodora@dblab.ece.ntua.gr" target="_blank">theodora@dblab.ece.ntua.gr</a>&gt; έγραψε:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
  
    
  
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    <div class="m_8567899577903856240m_3988535163947673014moz-cite-prefix m_8567899577903856240gmail_msg">Ένα σύνολο συσχετίσεων συνδέει δύο (ή
      περισσότερα) σύνολα οντοτήτων.<br class="m_8567899577903856240gmail_msg">
      Δεν μπορεί ένα σύνολο συσχετίσεων να συνδέει άλλα σύνολα
      συσχετίσεων μεταξύ τους.<br class="m_8567899577903856240gmail_msg">
      <br class="m_8567899577903856240gmail_msg">
      On 5/11/2016 8:15 μμ, John Sig wrote:<br class="m_8567899577903856240gmail_msg">
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        <div id="m_8567899577903856240m_3988535163947673014yui_3_16_0_ym19_1_1478368337718_29673" class="m_8567899577903856240gmail_msg">Καλησπέρα,<br class="m_8567899577903856240gmail_msg">
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                                    <div id="m_8567899577903856240m_3988535163947673014yiv3028243825yui_3_16_0_ym19_1_1478368337718_16478" style="color:#000;background-color:#fff;font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="m_8567899577903856240gmail_msg">
                                      <div dir="ltr" id="m_8567899577903856240m_3988535163947673014yiv3028243825yui_3_16_0_ym19_1_1478368337718_2420" class="m_8567899577903856240gmail_msg">είναι
                                        δυνατόν στο μοντέλο ER να έχουμε
                                        συσχέτιση συσχετίσεων,</div>
                                      <div dir="ltr" id="m_8567899577903856240m_3988535163947673014yiv3028243825yui_3_16_0_ym19_1_1478368337718_2420" class="m_8567899577903856240gmail_msg">δηλαδή
                                        μία οντότητα να συνδέει μία
                                        συσχέτιση με μία άλλη συσχέτιση;</div>
                                      <div dir="ltr" id="m_8567899577903856240m_3988535163947673014yiv3028243825yui_3_16_0_ym19_1_1478368337718_2420" class="m_8567899577903856240gmail_msg"><br clear="none" class="m_8567899577903856240gmail_msg">
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      <pre class="m_8567899577903856240gmail_msg">______________________________<wbr>_________________
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