Related documents. Questions 1 and 2 can be done at any time, and should be turned in at the end of the test along with all of the front matter in the test. Boundary d. Optimal d. a. 0000002009 00000 n 1. What is UML?? Submitted by Monika Sharma, on November 09, 2019 . 0000008818 00000 n UML interview questions: UML (Unified Modeling Language) has been spreading its roots among the designing and visualization part. OOAD MCQs (Multiple Choice Questions Answers) 1. x��VKoE�aCփ�\��0���ci:]���"!$�%�JN�$B8�����U��L��^?��������j�&����W�ͳ�Ծ���j�1��\�U�_5�o��������]C�|��Lg}u�_�4�ϛ��ޥ�,>y�������Oڅի����k�~u���A��z��o7��Hz|�/%�bKɕ���:�z�D������Å���3:���JĆS��Am�U�혭 ꡬ)��ZW�Z簒�|W�FX]�:�&��ԧ��bq�q$��k/�[�踳��K��u"�-��u�u����͏��`$�Ž��(�� e:�)k+8�͟�I�&����HD��2�%|p����zZͻ��l����~J *��{ �]�cLP�. Should you decide to answer four questions… This field has a lot for the potential seekers and the individuals interested in the The number of sequences for which you correctly identify the processes and select the right variant will equal your final score. [4 marks] The sides of a square are 16 cm in length. 0000002519 00000 n Starting with question 3 on this exam, each question builds on the answer from the previous question. sequence of DFDs that is usually followed when modeling systems. The pattern is that every number is eight more than the last. _���R�@j��X/�5:q��ͨOhJ�D#:]6�a ��'I:�� J� �����0f�AR� Y�z8,��ۂ6�*�=�tE�8T�g�9����X�g� �ׇ��q�9W1��$�w�V�^nd�{�5g���ܶ�lE�`������]�O��/��z��*{~Y5�=l�Q>�P;��/�Jy��ה^us�8xʕ>��'`�u�1��!��/:�^m�9�s&��1J �([�.x�ʜn?,OZ��I֡ܢu^;'�X�Dz�9LՃ�s�Z\�ݍ��ܮJ��o�=�z'��::�W�H���*�X����/�;�g��kW����� This classifier is known as context classifier, which provides the context for interaction. This is both a sequence of increasing complexity and sophistication, and also the Examples of UML diagrams - website, ATM, online shopping, library management, single sign-on (SSO) for Google Apps, etc. H�l�In1E�>E�� D�"�� ��7���|M]R�a؀�9S�,���Kk�(~�����C�?qYQR�� �D�h\5�D��z� ����2H��̉ů�N��x�̐F�"�� �"��D�6S蔺�a�� ~�iӅ9'�Ԋt*Y ܉{���f��a*]� �LI(`%-��@��N���W�b� Yn� )�,��ܱ��P}�e��X@O|#���N�^ 0000003652 00000 n Let denote the length of one of the equal sides of each new triangle. trailer << /Size 164 /Info 107 0 R /Root 110 0 R /Prev 100368 /ID[<6b335f8ea3dcb6aab04d0d54f667e31a><6b335f8ea3dcb6aab04d0d54f667e31a>] >> startxref 0 %%EOF 110 0 obj << /Type /Catalog /Pages 108 0 R /Outlines 113 0 R /Names 111 0 R /OpenAction [ 112 0 R /XYZ null null null ] /PageMode /UseOutlines >> endobj 111 0 obj << /Dests 106 0 R >> endobj 162 0 obj << /S 155 /O 255 /E 271 /Filter /FlateDecode /Length 163 0 R >> stream What classes can be created from this?The answers to these questions provide a number of potential classes, which we model in a first draft of the class diagram. The object-oriented development life cycle is which of the following? UML Multiple Choice Questions and Answers PDF Experienced Freshers. Sequence Diagrams, State Machine Diagrams and Activity Diagrams Exercise 1 Consider the UML diagram shown below and answer the questions that follow it. The client first sends all unsent email to the server. Question 9 AD001. Analysis, design, and Sol. Structural, behavioral, architectural 3. • Easier to do sequence diagrams as a team. The UML defines several forms of interaction diagram, of which the most common is the sequence diagram. 2. Consultation 2. 0000013084 00000 n super helpful. The standard is managed, and was created by, the Object Management Group. One then goes to a doctor and after consultation with him, under goes treatment to finally attain recovery. 0000006095 00000 n ڳ� ��D?�5���g �7�}�L���V\��7�Q�J��O���2T��R�O|�J�q[�&1����BP�|�+�7i�%V|�4wa���QZ!r���C�~�{&n�16:F+���Pk���(3F6��g:Ժf>��cs�/�]ѻ��WӖ>7y�w�����^-^��r�b~b��� To hide the internal implementation of an object we use … The user presses the “check email” button. (a) What kind of diagram is this and what are such diagrams usually used to represent? Diagrammatic reasoning tests consist of diagram-based sequences and usually have four answer options. *�Ϙs��T$sFN-!��z�C�/W��M'�؁EN �Ϩ-��WJ�$��n��GJ�D�%�b��"���|J e%>2��AEh��!�J|$;K:Һب��)1�2��e��Vi19KNлTK�m��\�L�Ͱ0�jY)b��aаT�)r2]q#�QV�F�tK��z�;��"y��q�+&�a>W9)�#� �)�(�I�()\q'i��i�_ ��� endstream endobj 152 0 obj << /Type /FontDescriptor /Ascent 720 /CapHeight 663 /Descent -270 /Flags 34 /FontBBox [ -183 -269 1099 851 ] /FontName /AGaramond-Regular /ItalicAngle 0 /StemV 74 /XHeight 397 >> endobj 153 0 obj << /Type /Font /Subtype /Type1 /FirstChar 32 /LastChar 181 /Widths [ 250 220 404 500 500 844 818 235 320 320 394 500 250 320 250 327 500 500 500 500 500 500 500 500 500 500 250 250 500 500 500 321 765 623 605 696 780 584 538 747 806 338 345 675 553 912 783 795 549 795 645 489 660 746 676 960 643 574 641 320 309 320 500 500 360 404 500 400 509 396 290 446 515 257 253 482 247 787 525 486 507 497 332 323 307 512 432 660 432 438 377 320 239 320 500 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 235 0 0 0 0 0 0 0 0 0 0 0 0 0 250 0 500 500 0 0 0 0 0 790 0 0 0 320 0 0 0 500 0 0 0 512 ] /Encoding /WinAnsiEncoding /BaseFont /AGaramond-Regular /FontDescriptor 152 0 R >> endobj 154 0 obj << /Type /Font /Subtype /Type1 /FirstChar 32 /LastChar 181 /Widths [ 255 280 438 510 510 868 834 248 320 320 420 510 255 320 255 347 510 510 510 510 510 510 510 510 510 510 255 255 510 510 510 330 781 627 627 694 784 580 533 743 812 354 354 684 560 921 780 792 588 792 656 504 682 744 650 968 648 590 638 320 329 320 510 500 380 420 510 400 513 409 301 464 522 268 259 484 258 798 533 492 516 503 349 346 321 520 434 684 439 448 390 320 255 320 510 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 510 510 255 255 255 255 255 800 255 255 255 255 255 255 255 510 255 255 255 522 ] /Encoding /WinAnsiEncoding /BaseFont /AGaramond-Semibold /FontDescriptor 155 0 R >> endobj 155 0 obj << /Type /FontDescriptor /Ascent 720 /CapHeight 663 /Descent -270 /Flags 262178 /FontBBox [ -177 -269 1123 866 ] /FontName /AGaramond-Semibold /ItalicAngle 0 /StemV 105 /XHeight 397 >> endobj 156 0 obj 674 endobj 157 0 obj << /Filter /FlateDecode /Length 156 0 R >> stream 2.4 on the screen in the order left → right. 0000003888 00000 n 0000004124 00000 n Fill in the boxes at the top of this page with your name, centre number and candidate number. 6, 11, 16, 21, 26 Find an expression, in terms of n, for the nth term of the sequence. So students should practice these venn diagram questions and answers to get better ranks in their exams. 0000007972 00000 n Only one submission is needed per student team. What are the three types of modeling in UML? 0000001987 00000 n A msg1 B msg2 msg3 C b) The class diagram above is consistent with the sequence diagram. Select a quiz, set the number of questions you want to play and you're ready to begin! Abstraction has _____ types. Students may choose a variety of situations to use for the nth level data flow diagrams for this answer. ��.��S%T� �T ��XZ��jq�Ƚ[=���9`ݭ��Z�7QW�H��lS/0����̷��-wZw']e��#W6!�n! Select one: a. a) Answer The class diagram above is consistent with the sequence diagram. ok. PL. Question 10 In UML deployment diagrams (indicate all correct answers): UML sequence diagrams •sequence diagram: an “interaction diagram” that models a single scenario executing in the system –one of the most common UML diagrams Representing objects •An object: a square with object type, H�l�;�;E�^��Q")j=���WR�B7�����ԫ ���c�d��~�1HK_d�I��u#�~�^6�r�!��o+&�I:�ˊI�����B�jσ�ٕϘvd!�3L�D\A6����ϯ��BV돩�����Kؑ�!�C•�R���0D[� Define Sequence Diagram? Flawed sequence diagram 1 19 What’s wrong with this sequence diagram? Exam 2015, questions and answers University Charles Sturt University Course System Analysis PG (ITC412) Academic year 2014/2015 Helpful? The process is repeated twice, as shown in diagrams 2 and 3. 4. endstream endobj 142 0 obj 665 endobj 143 0 obj << /Filter /FlateDecode /Length 142 0 R >> stream Sequence diagram can be drawn at different levels of detail and also to meet different purposes at several stages in the development life cycle. Sequence diagram shows an interaction between objects arranged in a time sequence. Unified Modeling Language (UML) Interview Questions and Answers will guide us that UML is a standardized general-purpose modeling language in the field of software engineering. UML provides neither notation to model exception handling in sequence diagrams nor any reasoning why it is absent. 6 0 obj 0000004006 00000 n 2. x��RMo1��">J�9�L� v�8��!qk5R�S������%�v�b2�yrl�{~����D�u����y�7��*@�g9!��G�����pqoF_�Mmm������p W�*�ߔ;�E8��שu]����u_-��h�%֚���:�1Y�mo�̑j�N��sz0,0#���pX�'�)Sz4�R���e�>��ve��J�N�؛�*��*����.k�� (a) Clearly illness occurs first. %�쏢 0000004832 00000 n The message flow is shown vertically in waterfall manner i.e. Theodore• 3 months ago. 0000003540 00000 n �&b��� V�j��n��0�+�K5�������SG���aխOيA��5wN2��>rz��n9�&!�O�$��9�w�f��$8��G������e�����Ǿ{��c��urrfX�c.�Q��qA�r����W�/�\�|�C�3 €"ajay�r�Q���iE$FX�c.��QqL\�������O��:i|��?���俽�O� ��O endstream endobj 150 0 obj 600 endobj 151 0 obj << /Filter /FlateDecode /Length 150 0 R >> stream The Sequence and Series Test of Logical Reasoning Problem s and Solutions is available here. She then prepares the exam paper (with sample solutions), gets it copied to produce enough copies for the class, and hands it out to students on the designated time and location. stream Mǟ l�؟$b�['SOHQ��K�$\�A��7���˪5�J�j��Q��q�����w�$��Ţ�e����c��b�f#!����Q�Wr��\�_ɑ�:c%�T�&�7,�lR�MV��_~�Z���Vg�A���ݎ �Bak"��r��c�#��D���7�4ؤ�&��R����cю�8)��)�K�sR"�S�!��7q�b�����|���O�ݟR4g'%�H�*�$��h1�s����A���ރ�A�nb}��� �%6�\H�+����ޜa[�慖@c6rY�7�E9�\{9*͍�m����qj�M�Mx9l鸭�YP�g�!H���b�Zݎ�w����v�S��R�Z�_���I�������4\�nYG� Place both student names at the top of the page. 0000014349 00000 n Exam 2015, questions and answers. endobj (Total 2 marks) 2. sequence only is called the sequence network of that particular sequence. 0000004478 00000 n Submit a PDF containing your written responses to questions 1 - 4, and 5, and an image of the sequence diagram you created for questions 5 & 6. %PDF-1.3 There are several proposed notations for exception han Problems and Exercises Solutions 1. An analysis of the interrelationships, information needs, and actors and prototypes is conducted on the basis of general domain knowledge, discussions with experts, and documents. Below figure 'Sequence diagram' shows how a sequence diagram looks like. Graphical language for visualizing artifacts of the system.? In a sequence Here are the correct answers to all questions: 1. b 2. d 3. a 4. b 5. b 6. a 7. d 8. b 9. d 10. b c 11. b d 12. d 13. b c 14. b 15. a 16. b 17. a 18. b d 19. a 20. d Give yourself 1 point for each correctly answered question (for multiple answer ques-tions, this means that all correct answers … 0000013860 00000 n The 2.0 version of UML changed Sequence Diagrams significantly, the expressiveness of the language was highly increased. 29 + 8 = 37. Here are some examples: 0, 2, 4, 6, 8 12, 14, 16, 18, 20 100, 102, 104, 106, 108 Illness; Doctor 4. Introduction The following five quizzes help to test your knowledge about the class diagram, sequence diagram, state machine diagram, activity diagram and use case diagram. Only one submission is needed questions up to two points each; Part II: 4 modeling questions up to 20 points each. 0000006301 00000 n System Analysis PG (ITC412) Academic year. If you start from the answer options and work backwards, you are 0000003770 00000 n 1.who consider diagrams as a type of Class diagram, component diagram, object diagram… Question 82. Elements involved •Actor 0000003309 00000 n . but also all subsequent sequences concerning that variation including any validation sequences, responses to questions, closing sequence s etc.)? What is UML Architecture? [Short Questions; continued] (c) [Use Case Diagrams – 5 marks] Draw a use case diagram for exams for undergraduate Computer Science courses such as this. (ee diagrams in … Two d. The objective function is maximised approach labelled as operations research (or operational research), management A number of sources, including company reports and … ? 40 3 Share Comments Please sign in or register to post comments. Starting with question 3 on this exam, each question … 30/08/2019 Self-test OOAD/UML 2 INTRODUCTION TO THE SELF-TEST OOAD/UML With this test you can see for yourself if you attained the objectives of the OOAD/UML course (or if … For this goal, we will learn to write textual descriptions as well as to draw complementary UML diagrams (such as sequence or activity diagrams). 0000004950 00000 n English Enhanced Scope and Sequence Lesson Skill: Identifying elements of plot structure Strand Reading—fiction SOL 6.5 7.5 8.5 Materials • A fiction book that students have read and that follows the basic plot structure <> PLC MCQ, Programmable Logic Controllers Examples, PLC Programs, PLC Tutorials, PLC Ladder Logics, PLC Theory. ������3�.RۈK����ɜ�y�ȩ���4�>9��h�G���6|v��G;2��aM *��H���S�6� gr?�����tk��ɶ��&�CS���T7�j���"ft���= �E� Basically, students should continue the process of decomposition until they have reached the point where no sub-process can logically be broken down further (i.e., each process meets the definition of a primitive process). PRE-TEST QUESTIONS The answers to these questions are in Appendix A at the end of this manual. 1. 0000008796 00000 n PLC Interview Questions and Answers. }w��:9��L���3�xC6f�b�����iz�n?�q��49�2��w University. 2.3 describes the norm()function. "T�&L�(�Z�61���(YhXE�d�d�/0�����k&�k8���XDI�&s�I��o2lT5�{!����K�A�4o���3Vyu�)O�TW=���J>�̾�����ڠMk|�W|j3������})����%z��Z�S�qn���E�M���?�a�~���g� ֖-iܲ�VH������b��,kfJ–"g��4�Ҍ�Evpͱ��l['�Cf�=qV� ��G��x��M�CP���5���{6h�ٻ�]]��֠��\��>��d�a�T��[�`2�iXQ��3D.ï#Q}�����QZ�J�!�g���d6�t���fٽIJ��0�$)&�xH 18 0 obj Endale• 1 year ago. 0000001612 00000 n Some time Reasoning questions are very confusing and time consuming and candidates face problem in this section as they find it difficult to finish it on time. 0000010453 00000 n Then we will see how to specify the functional view by explaining in detail the different ways in which actors can use the system. 2014/2015. What Do You Mean By Focus Of Control? Tracing paper may be used. Using the example of a retail clothing store in a mall, list relevant data flows, data stores, processes, and sources/sinks. I found this document helpful. Abstraction has _____ types. 0000002718 00000 n is a sequence of numbers alternating between 1 and −1. Treatment; Recovery (a) 2 3 14 5 (b) 23415 (c) 43 12 5 (d) 5 1432 . 0000009635 00000 n Examine the sequence to find a pattern. 0000014428 00000 n Title Logical Reasoning Questions and Answers Author JobTestPrep.co.uk Subject Logical Reasoning Questions and Answers with Explanations Keywords logical reasoning questions and answers pdf, inductive reasoning questions There is a use case and system sequence diagram for the remaining questions following the first two questions. Here are the first five terms of a number sequence… High coupling makes the design easy to understand b. it starts from the top and flows to the bottom. Your score will be given to you raw, and as a … Instructions Use black ink or ball-point pen. �E���䯎��W�>7��� o]ٌ endstream endobj 146 0 obj 737 endobj 147 0 obj << /Filter /FlateDecode /Length 146 0 R >> stream Submit a PDF containing your written responses to questions 1 - 4, and 5, and an image of the sequence diagram you created for questions 5 & 6. The interactions are simply units of the behavior of a classifier. �ф� s�L�dΏ��Z������˻Ss��͜�~>��݉ �|?���H�@�z���P׼��]��F|���=8�R��B���� ��T��LN2`ɐ�l���GsY�9$3WJ~�d�96��^! Which of the following is not true Select one: a. UML Interview Questions and Answers will discus that UML includes a set of graphical notation techniques … Sequence boundaries can in this case only be identified by the petrographic and mineralogical manifestos such as encrustations, hardpans etc… attesting to … • Can see many objects/classes at a time on same page (visual bandwidth). In this sequence diagram we have four objects 'Customer','Product','Stock' and 'Payment'. Do not submit zip file. Share. 0000004242 00000 n <> Question 81. A sequence of five consecutive even numbers is a sequence of even numbers such that the difference between one number and the next is always 2. OOAD MCQs (Multiple Choice Questions Answers) 1. 1. 0000007205 00000 n 0000011155 00000 n This process . Download PDF. 53 Chapter 4 Sequence Diagrams Interaction diagrams describe how groups of objects collaborate in some behav-ior. At the page Login you can easily create a user and then also save played quizzes and practice questions using a cardbox system. In this sequence diagram we have four objects 'Customer','Product','Stock' and 'Payment'. UML - Statechart Diagram UML - Activity Diagram UML - Summary UML 2.0 Overview UML 2.0 - Overview UML Useful Resources UML - Useful Resources UML - Knowledge Test Utilities UML - Tools & Utilities UML - Discussion • Sequence diagrams are language-agnostic (can be implemented in many different languages) • Non-coders can read and write sequence diagrams. SEQUENCES Materials required for examination Items included with question papers Ruler graduated in centimetres and Nil millimetres, protractor, compasses, pen, HB pencil, eraser. High coupling makes it harder to … 06:16:00 / by Interview questions answers pdf / in UML Multiple Choice Questions and Answers PDF Experienced Freshers / with No comments / Read the most frequently asked 19 top UML multiple choice questions and answers PDF for freshers and experienced. Place both student names at the top of the page. Observe several sales transactions. Sequence diagram from a use case 6 1. In each case, the dots written at the end indicate that we must consider the sequence as an infinite sequence, so that it goes on for ever. ?,F����4��G'������w��?ޯIzP0��Ca����f_�L�x� ߜ �������N����I�>6Rl1�P" A��9�/��8�9���$F���ZW�n%�y1���:�MǴ�q�>o���H��}5�Ϝ�` ڪ�u]�[��4é$e]�5���ڨ���xE�tP*�s�:�/~'i B. The numbers 1, 3, 5, 9 form a finite sequence containing just four numbers. ;鵎D�����D����8Tb!��H %q���kRҖ@�ϣ��VL��k����|���'��/�Smc���}=���, OB��G������˒�������6����� ����b�� :M/cu�ĵ����s$����|����$"0�b�Wr����#��jX��bi k{J� ���R�/��*��w�%�,Տ����b��%�6f3)���J��aw� �j��y@>����PC�>��닊����l�����-�h�B)�����r��ŵ�c�����Jj��&"%vH�ux\,���2R��|-$w�B� ���8z�4ya��h����[�|3ȅ�x֍ 졹&�;7�_*�� 1A����t��jO�,]W�RKȪ�Z����Q�"#�.F��== KU�Dv���3��$������z��u"��Y O�e^#�R�rc�h�* ��$0r8�h�2�u����73��ŋ�h���d���e���ȥ��K߉MJb�y��F%��=)#s�N�"e�_� )��! H�t�Mo1���+r�"�&N��#T����`o�SE��=����$�ժ�v�ԯ�:cg�y�n? Course. During this unit we shall investigate each of the three types of diagram in the sequence they are described above. The message flow is shown vertically in waterfall manner i.e. Peter• 7 months ago. -�uٟJy�]�b/�D?�Ǭ>��$&$����R�&($�˂2_�Eٷ� i˚��̒�!l��tЕ��Z�3i �~!�{�χQjX�|_�$~1��*5?�����Lq�|B��#Є����I�Q�ۋ6|}n�xЦ�mM���=��Ղ5����a�..3,���m+Þ�oH֦Ýy���I�Om!�K��ھX�U)厽�&�7��^�vY��֎I{� 9��� endstream endobj 158 0 obj 409 endobj 159 0 obj << /Filter /FlateDecode /Length 158 0 R >> stream 0000003427 00000 n 0000007183 00000 n The midpoints of the sides of this square are joined to form a new square and four triangles (diagram 1). These are in the mode of multiple choice bits and are also viewed regularly by ssc, postal, railway exams aspirants. Sequence Diagrams, State Machine Diagrams and Activity Diagrams Exercise 1 Consider the UML diagram shown below and answer the questions that follow it. Let us see the UML Diagrams MCQs Questions Answers. please combine the two sequence diagrams into a single sequence diagram. 1. Quiz is useful for IBPS clerks, PO, SBI clerks, PO, insurance, LIC AAO and for all types of banking exams with pdf. 0000012848 00000 n 0000002614 00000 n a) 1 b) 2 c) 3 d) 4 2. 0000009657 00000 n 3. 1. 0000005306 00000 n stream Let us see the UML diagrams solved MCQs Questions Answers. %PDF-1.2 %���� 0000003090 00000 n )�A`:�\��ƎHmc��ye��3��� 2ݟ endstream endobj 148 0 obj 716 endobj 149 0 obj << /Filter /FlateDecode /Length 148 0 R >> stream H��UMO1���cǤM����Y�����f$�(`b��δ� �=x��i���7i\�Z�C�F��J�&�iVB�:}V���W(� �����`ho�2�r�u�k�H�z^�l)�v�^�m�|_�}2��>���}Oi\��R ��Ta4�g�[֔�zE)P�=�V�y��`h��������}���Rs�7N��~"+�dC�(읺��S�ެ�_�����0�>/���/. 1.Use case descriptions consist of interaction_____? There is a use case and system sequence diagram for the remaining questions following the first two questions. What is a sequence diagram? An interaction is defined as a Add to find the next number. ���C�d�N��9y3nH��LV�)�ƨ�k���њ��xz���~��|�~ 109 0 obj << /Linearized 1 /O 112 /H [ 1653 356 ] /L 102678 /E 14660 /N 10 /T 100379 >> endobj xref 109 55 0000000016 00000 n 0000002390 00000 n How many views of the software can be represented through the Unified Modeling Language (UML)? a. sequence and communication diagrams b. sequence and activity diagrams c. class and composite structure diagrams d. use-case and activity diagrams Show Answer. 0000004360 00000 n 9a. d) Answer Message msg2 is sent after msg1 has been received. Please sign in or register to post comments. The following five quizzes help to test your knowledge about the class diagram, sequence diagram, state machine diagram, activity diagram and use case diagram. !51�t��˖���Ǵ��7LU1�^9�kyz$\4�D������Β��0��u1���?������vq����]u�|����#�s51�Z Sequence Diagrams are time focus and they show the order of the interaction visually by using the vertical axis of the diagram to represent time what messages are sent and when. 0000006323 00000 n A 1.3: Yes, this element must be populated for ALL sequences which will be submitted for the particular variation or extension concerned. UML Diagrams Examples Examples by Technology or Application Domain Online shopping UML diagrams
2020 sequence diagram questions and answers pdf