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Annotation of 43BSDReno/contrib/isode-beta/doc/ftam/filestore.tex, revision 1.1

1.1     ! root        1: % run this through SLiTeX with the appropriate wrapper
        !             2: 
        !             3: \begin{bwslide}
        !             4: \part  {THE VIRTUAL FILESTORE}
        !             5: 
        !             6: \begin{nrtc}\bf
        !             7: \item  PHILOSOPHY
        !             8: 
        !             9: \item  FILE ATTRIBUTES
        !            10: 
        !            11: \item  ACTIVITY ATTRIBUTES
        !            12: 
        !            13: \item  DOCUMENT TYPES
        !            14: \end{nrtc}
        !            15: \end{bwslide}
        !            16: 
        !            17: 
        !            18: \begin{note}\em
        !            19: this section corresponds roughly to iso/dis 8571/2,
        !            20: but the concepts are explained in almost an entirely different way
        !            21: 
        !            22: this description is done via successive refinement:
        !            23: concepts are introduced and continuously expanded
        !            24: 
        !            25: hopefully,
        !            26: this is less intimidating than the way the standard presents things$\ldots$
        !            27: \end{note}
        !            28: 
        !            29: 
        !            30: \begin{bwslide}
        !            31: \part* {PHILOSOPHY}\bf
        !            32: 
        !            33: \begin{nrtc}
        !            34: \item  AS WITH ALL ``OPEN SYSTEM'' SERVICES
        !            35:     \begin{nrtc}
        !            36:     \item      DESCRIBES A CONCEPTUAL MODEL OF THE VIRTUAL SERVICE
        !            37: 
        !            38:     \item      SPECIFIES THE SERVICE AND THE PROTOCOL\\
        !            39:                INDEPENDENT OF ACTUAL LOCAL SYSTEMS
        !            40:        \begin{nrtc}
        !            41:        \item   PROGRAMATIC INTERFACES ARE NOT SPECIFIED
        !            42:        \end{nrtc}
        !            43:     \end{nrtc}
        !            44: 
        !            45: \item  THE FUNDAMENTAL ABSTRACTION: THE VIRTUAL FILESTORE
        !            46: 
        !            47: \item  A CONCEPTUAL MODEL OF A FILE SERVICE ON A LOCAL SYSTEM (LOCALSTORE)
        !            48: 
        !            49: \item  DIFFICULT TASK~---~EXISTING FILE SERVICES ARE QUITE DIFFERENT
        !            50: 
        !            51: \item  POTENTIALLY VERY REWARDING!
        !            52: \end{nrtc}
        !            53: \end{bwslide}
        !            54: 
        !            55: 
        !            56: \begin{bwslide}
        !            57: \ctitle        {RELATIONSHIP OF THE VIRTUAL FILESTORE\\ AND LOCALSTORE}
        !            58: 
        !            59: \vskip.5in
        !            60: \diagram[p]{figure1}
        !            61: \end{bwslide}
        !            62: 
        !            63: 
        !            64: \begin{note}\em
        !            65: why a virtual filestore?
        !            66: 
        !            67: it is unacceptable to choose any existing real filestore as the basis
        !            68: for the file service (all lack one thing or another)
        !            69: 
        !            70: hence, it is desirable to devise a model which can reasonably express any
        !            71: existing real filestore.
        !            72: \end{note}
        !            73: 
        !            74: 
        !            75: \begin{bwslide}
        !            76: \ctitle        {ELEMENTS}\bf
        !            77: 
        !            78: \begin{nrtc}
        !            79: \item  A (VIRTUAL) FILESTORE IS A COLLECTION OF FILES
        !            80: 
        !            81: \item  A FILENAME IDENTIFIES EXACTLY ONE FILE IN THE FILESTORE
        !            82: 
        !            83: \item  THERE IS NO EXPLICIT RELATIONSHIP BETWEEN DIFFERENT FILES IN THE
        !            84:        FILESTORE
        !            85:     \begin{nrtc}
        !            86:     \item      i.e., NO DIRECTORY STRUCTURE (A {\bf BIG} MISTAKE)
        !            87:     \end{nrtc}
        !            88: 
        !            89: \item  FILES HAVE
        !            90:     \begin{nrtc}
        !            91:     \item      ATTRIBUTES (e.g., OWNERSHIP INFORMATION)
        !            92: 
        !            93:     \item      CONTENTS (e.g., RANDOM-ACCESS RECORDS)
        !            94:     \end{nrtc}
        !            95: \end{nrtc}
        !            96: \end{bwslide}
        !            97: 
        !            98: 
        !            99: \begin{bwslide}
        !           100: \ctitle        {ELEMENTS -- ATTRIBUTES}
        !           101: 
        !           102: \begin{nrtc}
        !           103: \item  TWO KINDS OF ATTRIBUTES ARE DEFINED
        !           104: 
        !           105: \item  FILE ATTRIBUTES, WHICH EXIST ON A PER-FILE BASIS
        !           106:     \begin{nrtc}
        !           107:         \item  SIMULTANEOUS CLIENTS OF THE FILESTORE SEE THE SAME INFORMATION
        !           108: 
        !           109:        \item   e.g., THE NAME OF THE FILE
        !           110:     \end{nrtc}
        !           111: 
        !           112: \item  ACTIVITY ATTRIBUTES, WHICH EXIST ON A PER-CLIENT BASIS
        !           113:     \begin{nrtc}
        !           114:     \item      INTERACTIONS BY A CLIENT ARE NOT DIRECTLY VISIBLE TO OTHER
        !           115:                CLIENTS
        !           116: 
        !           117:     \item      e.g., HOW THE FILE IS BEING TRAVERSED
        !           118:     \end{nrtc}
        !           119: 
        !           120: \item  THE CLIENT INTERACTS ON AT MOST ONE FILE
        !           121:     \begin{nrtc}
        !           122:     \item      THE ``SELECTED'' FILE
        !           123:     \end{nrtc}
        !           124: \end{nrtc}
        !           125: \end{bwslide}
        !           126: 
        !           127: 
        !           128: \begin{bwslide}
        !           129: \ctitle        {ELEMENTS -- CONTENTS}
        !           130: 
        !           131: \begin{nrtc}
        !           132: \item  TYPICALLY, FILES ARE DEFINED IN TERMS OF A ``DOCUMENT TYPE''
        !           133: 
        !           134: \item  STATIC CHARACTERISTICS
        !           135:     \begin{nrtc}
        !           136:     \item      THE COMPOSITION OF THE FILE IN TERMS OF FILE ACCESS DATA
        !           137:                UNITS (FADUs)\\
        !           138:                e.g., A SEQUENTIAL COLLECTION OF RECORDS
        !           139: 
        !           140:     \item      THE STRUCTURE OF EACH DATA UNIT (DUs)\\
        !           141:                e.g., EACH RECORD CONTAINS A PERSONNEL RECORD
        !           142:     \end{nrtc}
        !           143: 
        !           144: \item  DYNAMIC CHARACTERISTICS
        !           145:     \begin{nrtc}
        !           146:     \item      HOW DATA UNITS ARE ENCODED ON THE NETWORK
        !           147: 
        !           148:     \item      HOW DATA UNITS ARE REFERENCED (e.g., CURRENT POSITION)
        !           149:     \end{nrtc}
        !           150: \end{nrtc}
        !           151: \end{bwslide}
        !           152: 
        !           153: 
        !           154: \begin{bwslide}
        !           155: \part* {FILE ATTRIBUTES}\bf
        !           156: 
        !           157: \begin{nrtc}
        !           158: \item  FOUR GROUPS OF FILE ATTRIBUTES
        !           159: 
        !           160: \item  KERNEL GROUP (REQUIRED)
        !           161:     \begin{nrtc}
        !           162:     \item      NECESSARY FOR FILE SELECTION AND BASIC FILE TRANSFER
        !           163:     \end{nrtc}
        !           164: 
        !           165: \item  STORAGE GROUP (OPTIONAL)
        !           166:     \begin{nrtc}
        !           167:     \item      DESCRIBES THE STORAGE CHARACTERISTICS FOR THE FILE
        !           168:     \end{nrtc}
        !           169: 
        !           170: \item  SECURITY GROUP (OPTIONAL)
        !           171:     \begin{nrtc}
        !           172:     \item      DESCRIBES THE ACCESS CONTROL MECHANISMS FOR THE FILE
        !           173:     \end{nrtc}
        !           174: 
        !           175: \item  PRIVATE GROUP (OPTIONAL)
        !           176:     \begin{nrtc}
        !           177:     \item      A MECHANISM TO CAPTURE NON-STANDARD (PROPRIETARY)
        !           178:                MECHANISMS THAT CAN NOT BE OTHERWISE REPRESENTED
        !           179:     \end{nrtc}
        !           180: \end{nrtc}
        !           181: \end{bwslide}
        !           182: 
        !           183: 
        !           184: \begin{note}\em
        !           185: definitions of types is rather loose at this point in the presentation;
        !           186: e.g., ``string'' is usually an asn.1 graphicstring
        !           187: 
        !           188: the emphasis at the moment is on the concept,
        !           189: not on the actual abstract data type
        !           190: \end{note}
        !           191: 
        !           192: 
        !           193: \begin{bwslide}
        !           194: \ctitle        {KERNEL GROUP}
        !           195: 
        !           196: \begin{nrtc}
        !           197: \item  FILENAME: A SEQUENCE OF STRINGS
        !           198:     \begin{nrtc}
        !           199:     \item      MAPPING TO THE LOCALSTORE NAMING CONVENTIONS IS A
        !           200:                ``LOCAL IMPLEMENTATION CHOICE''
        !           201:     \end{nrtc}
        !           202: 
        !           203: \item  CONTENTS TYPE: STRUCTURING INFORMATION
        !           204:     \begin{nrtc}
        !           205:     \item      THE FILE STRUCTURE (A {\bf LOT} MORE LATER)
        !           206:     \end{nrtc}
        !           207:        
        !           208: \end{nrtc}
        !           209: \end{bwslide}
        !           210: 
        !           211: 
        !           212: \begin{bwslide}
        !           213: \ctitle        {STORAGE GROUP}
        !           214: 
        !           215: \begin{nrtc}
        !           216: \item  STORAGE ACCOUNT: A STRING
        !           217:     \begin{nrtc}
        !           218:     \item      ENTITY ACCRUING FILE STORAGE CHARGES
        !           219:     \end{nrtc} 
        !           220: 
        !           221: \item  IDENTITY OF USER AND THE DATE/TIME OF
        !           222:     \begin{nrtc}
        !           223:     \item      FILE CREATION
        !           224: 
        !           225:     \item      LAST READ AND LAST MODIFICATION OF FILE CONTENTS
        !           226: 
        !           227:     \item      LAST MODIFICATION OF FILE ATTRIBUTES
        !           228:     \end{nrtc}
        !           229: 
        !           230: \item  FILE AVAILABILITY
        !           231:     \begin{nrtc}
        !           232:     \item      IMMEDIATE (FILE IS ``ON-LINE'')
        !           233: 
        !           234:     \item      DEFFERRED (ACCESS TO FILE MAY ENCOUNTER DELAY,
        !           235:                e.g., AWAITING ARCHIVE RETRIEVAL)
        !           236:     \end{nrtc}
        !           237: \end{nrtc}
        !           238: \end{bwslide}
        !           239: 
        !           240: 
        !           241: \begin{bwslide}
        !           242: \ctitle        {STORAGE GROUP (cont.)}
        !           243: 
        !           244: \begin{nrtc}
        !           245: \item  PERMITTED ACTIONS
        !           246:     \begin{nrtc}
        !           247:     \item      DESCRIBES THE TYPES OF DATA ACCESS THAT CAN BE PERFORMED ON
        !           248:                THE FILE
        !           249: 
        !           250:     \item      HOW DATA UNITS MAY BE ACCESSED
        !           251:                (READ, WRITE, EXTEND, etc.)
        !           252: 
        !           253:     \item      HOW THE FILE MAY BE TRAVERSED
        !           254:                (MOVING FROM ONE DATA UNIT TO ANOTHER)
        !           255:     \end{nrtc}
        !           256: 
        !           257: \item  FILESIZE (IN OCTETS)
        !           258:     \begin{nrtc}
        !           259:     \item      AN ESTIMATE OF THE TOTAL SIZE OF THE FILE'S CONTENTS
        !           260:     \end{nrtc}
        !           261:        
        !           262: 
        !           263: \item  FUTURE FILESIZE (IN OCTETS)
        !           264:     \begin{nrtc}
        !           265:     \item      A SOFT LIMIT ON THE TOTAL SIZE OF THE FILE'S CONTENTS
        !           266:     \end{nrtc}
        !           267: \end{nrtc}
        !           268: \end{bwslide}
        !           269: 
        !           270: 
        !           271: \begin{bwslide}
        !           272: \ctitle        {SECURITY GROUP}
        !           273: 
        !           274: \begin{nrtc}
        !           275: \item  ACCESS CONTROL (AN ACCESS CONTROL LIST)\\
        !           276:        FOR EACH ELEMENT OF THE LIST:
        !           277:     \begin{nrtc}
        !           278:     \item      FILE ACTIONS PERMITTED
        !           279: 
        !           280:     \item      ENTITY PERMITTED TO REQUEST ACTION (OPTIONAL)
        !           281: 
        !           282:     \item      PASSWORD REQUIRED TO VALIDATE ACTION
        !           283:     \end{nrtc}
        !           284: 
        !           285: \item  ENCRYPTION NAME
        !           286:     \begin{nrtc}
        !           287:     \item      DEFINES HOW FILE WAS ENCRYPTED
        !           288: 
        !           289:     \item      FILES ARE TRANSFERRED IN ENCRYPTED FORM
        !           290: 
        !           291:     \item      REQUIRES A REGISTRATION AUTHORITY TO BE ESTABLISHED
        !           292:     \end{nrtc}
        !           293: 
        !           294: \item  LEGAL QUALIFICATIONS
        !           295:     \begin{nrtc}
        !           296:     \item      DEFINES THE ``LEGAL STATUS'' OF THE FILE
        !           297: 
        !           298:     \item      MEANT TO BE USED WITH A NATIONAL PRIVACY LEGISLATION
        !           299:     \end{nrtc}
        !           300: \end{nrtc}
        !           301: \end{bwslide}
        !           302: 
        !           303: 
        !           304: \begin{bwslide}
        !           305: \ctitle        {PRIVATE GROUP}
        !           306: 
        !           307: \begin{nrtc}
        !           308: \item  A ``CATCH-ALL''
        !           309: 
        !           310: \item  USE IS STRONGLY DISCOURAGED
        !           311: \end{nrtc}
        !           312: \end{bwslide}
        !           313: 
        !           314: 
        !           315: \begin{bwslide}
        !           316: \part* {ACTIVITY ATTRIBUTES}\bf
        !           317: 
        !           318: \begin{nrtc}
        !           319: \item  ACTIVITY ATTRIBUTES ARE ALSO DEFINED IN TERMS OF GROUPS\\
        !           320:        KERNEL, STORAGE, AND SECURITY (NO PRIVATE GROUP, OBVIOUSLY)
        !           321: 
        !           322: \item  THESE ARE USUALLY INITIALIZED WHEN A FILE IS EITHER
        !           323:     \begin{nrtc}
        !           324:     \item      SELECTED
        !           325: 
        !           326:     \item      OPENED FOR TRANSFER/ACCESS
        !           327:     \end{nrtc}
        !           328: \end{nrtc}
        !           329: \end{bwslide}
        !           330: 
        !           331: 
        !           332: \begin{note}\em
        !           333: relationship of actions is rather loose at this point in the presentation;
        !           334: selection, open, transfer/access
        !           335: 
        !           336: the next section will formalize these terms
        !           337: \end{note}
        !           338: 
        !           339: 
        !           340: \begin{bwslide}
        !           341: \ctitle        {KERNEL GROUP ACTIVITY ATTRIBUTES}
        !           342: 
        !           343: \begin{nrtc}
        !           344: \item  ACTIVE CONTENTS TYPE
        !           345:     \begin{nrtc}
        !           346:     \item      THE CONTENTS TYPE
        !           347:     \end{nrtc}
        !           348: 
        !           349: \item  CURRENT ACCESS REQUEST
        !           350:     \begin{nrtc}
        !           351:     \item      THOSE PERMITTED ACTIONS WHICH ARE REQUESTED BY THE CLIENT
        !           352: 
        !           353:     \item      CONTENTS: READ, INSERT, REPLACE, EXTEND, ERASE
        !           354: 
        !           355:     \item      ATTRIBUTES: READ, CHANGE, AND DELETE FILE
        !           356:     \end{nrtc}
        !           357: 
        !           358: \item  CURRENT LOCATION
        !           359: 
        !           360: \item  CURRENT PROCESSING MODE
        !           361:     \begin{nrtc}
        !           362:     \item      ACTIONS ON THE CONTENTS WHICH THE CLIENT WISHES TO PERFORM
        !           363:                (READ, INSERT, REPLACE, EXTEND, ERASE, LOCATE)
        !           364:     \end{nrtc}
        !           365:        
        !           366: \item  CURRENT APPLICATION ENTITY TITLE
        !           367:     \begin{nrtc}
        !           368:     \item      A GLOBAL IDENTIFIER FOR THE ENTITY PROVIDING THE FILE SERVICE
        !           369:                (A FILESTORE OR FILESERVER)
        !           370:     \end{nrtc}
        !           371: \end{nrtc}
        !           372: \end{bwslide}
        !           373: 
        !           374: 
        !           375: \begin{bwslide}
        !           376: \ctitle        {STORAGE GROUP ACTIVITY ATTRIBUTES}
        !           377: 
        !           378: \begin{nrtc}
        !           379: \item  CURRENT ACCOUNT
        !           380:     \begin{nrtc}
        !           381:     \item      THE CLIENT'S ACCOUNT WHEN THE FILE SERVICE WAS INITIATED
        !           382:                (MAY BE CHANGED WHEN A FILE IS SELECTED)
        !           383:     \end{nrtc}
        !           384: 
        !           385: \item  CURRENT ACCESS CONTEXT
        !           386:     \begin{nrtc}
        !           387:     \item      HOW THE FILE STRUCTURE IS COMMUNICATED ON THE NETWORK
        !           388:                (MUCH MORE ON THIS LATER)
        !           389:     \end{nrtc}
        !           390: 
        !           391: \item  CURRENT CONCURRENCY CONTROL
        !           392:     \begin{nrtc}
        !           393:     \item      HOW SIMULTANEOUS CLIENTS INTERACT WHEN ACCESSING THE FILE
        !           394: 
        !           395:     \item      FOR EACH ACTION: SHARED, EXCLUSIVE, NOT REQUIRED, NO ACCESS
        !           396:     \end{nrtc}
        !           397: \end{nrtc}
        !           398: \end{bwslide}
        !           399: 
        !           400: 
        !           401: \begin{bwslide}
        !           402: \ctitle        {SECURITY GROUP ACTIVITY ATTRIBUTES}
        !           403: 
        !           404: \begin{nrtc}
        !           405: \item  ACTIVE LEGAL QUALIFICATION
        !           406: 
        !           407: \item  CURRENT INITIATOR IDENTITY
        !           408:     \begin{nrtc}
        !           409:     \item      THE CLIENT'S IDENTITY WHEN THE FILE SERVICE WAS INITIATED
        !           410:     \end{nrtc}
        !           411: 
        !           412: \item  CURRENT ACCESS PASSWORDS
        !           413:     \begin{nrtc}
        !           414:     \item      THE ACCESS LIST WHICH APPLIES TO THE CLIENT
        !           415:     \end{nrtc}
        !           416: \end{nrtc}
        !           417: \end{bwslide}
        !           418: 
        !           419: 
        !           420: \begin{bwslide}
        !           421: \part* {DOCUMENT TYPES}\bf
        !           422: 
        !           423: \begin{nrtc}
        !           424: \item  STATIC CHARACTERISTICS
        !           425:     \begin{nrtc}
        !           426:     \item      THE FILE ACCESS STRUCTURE (CONSTRAINT SET NAME)
        !           427: 
        !           428:     \item      THE PRESENTATION STRUCTURE (ABSTRACT SYNTAX NAME)
        !           429:     \end{nrtc}
        !           430: 
        !           431: \item  DYNAMIC CHARACTERISTICS
        !           432:     \begin{nrtc}
        !           433:     \item      THE TRANSFER STRUCTURE (TRANSFER SYNTAX NAME)
        !           434: 
        !           435:     \item      A IDENTIFICATION STRUCTURE (ACCESS CONTEXTS)
        !           436:     \end{nrtc}
        !           437: 
        !           438: \item  ``REGISTERED'' AND REFERENCED VIA A UNIQUE IDENTIFIER
        !           439: \end{nrtc}
        !           440: \end{bwslide}
        !           441: 
        !           442: 
        !           443: \begin{bwslide}
        !           444: \ctitle        {FILE ACCESS STRUCTURE}
        !           445: 
        !           446: \begin{nrtc}
        !           447: \item  ANY FILE'S CONTENT CAN BE DESCRIBED AS A TREE
        !           448: 
        !           449: \item  EACH NODE IN THE TREE CONTAINS
        !           450:     \begin{nrtc}
        !           451:     \item      A DESCRIPTOR (A NAME AND DISTANCE TO PARENT)
        !           452: 
        !           453:     \item      OPTIONALLY, A DATA UNIT (DEFINED BY THE PRESENTATION STRUCTURE)
        !           454: 
        !           455:     \item      OPTIONALLY, CHILDREN (OTHER NODES)
        !           456:     \end{nrtc}
        !           457: 
        !           458: \item  THE ROOT NODE DEFINES THE ``STARTING'' POINT FOR THE FILE
        !           459: 
        !           460: \item  NEED A WAY TO LIMIT THE COMPLEXITY OF THE TREE
        !           461: \end{nrtc}
        !           462: \end{bwslide}
        !           463: 
        !           464: 
        !           465: \begin{bwslide}
        !           466: \ctitle        {CONSTRAINT SETS}
        !           467: 
        !           468: \begin{nrtc}
        !           469: \item  DEFINES THE STRUCTURE OF THE TREE AND HOW ACTIONS ON THE FILE
        !           470:        (e.g., WRITE, ERASE) CHANGE THE STRUCTURE AND POSITION
        !           471: 
        !           472: \item  SEVERAL KINDS
        !           473:     \begin{nrtc}
        !           474:     \item      UNSTRUCTURED
        !           475: 
        !           476:     \item      SEQUENTIAL FLAT
        !           477: 
        !           478:     \item      ORDERED FLAT
        !           479: 
        !           480:     \item      ORDERED FLAT WITH UNIQUE NAMES
        !           481: 
        !           482:     \item      ORDERED HIERARCHICAL
        !           483: 
        !           484:     \item      GENERAL HIERARCHICAL
        !           485: 
        !           486:     \item      GENERAL HIERARCHICAL WITH UNIQUE NAMES
        !           487:     \end{nrtc}
        !           488: \end{nrtc}
        !           489: \end{bwslide}
        !           490: 
        !           491: 
        !           492: \begin{bwslide}
        !           493: \ctitle        {EXAMPLE: UNSTRUCTURED CONSTRAINT SET}
        !           494: 
        !           495: \vskip.5in
        !           496: \diagram[p]{figure2}
        !           497: \end{bwslide}
        !           498: 
        !           499: 
        !           500: \begin{note}\em
        !           501: a unnamed root node with a data unit but no children
        !           502: 
        !           503: file can be transferred as a whole, or extended
        !           504: 
        !           505: access to a part is not permitted
        !           506: \end{note}
        !           507: 
        !           508: 
        !           509: \begin{bwslide}
        !           510: \ctitle        {EXAMPLE: SEQUENTIAL FLAT CONSTRAINT SET}
        !           511: 
        !           512: \vskip.5in
        !           513: \diagram[p]{figure3}
        !           514: \end{bwslide}
        !           515: 
        !           516: 
        !           517: \begin{note}\em
        !           518: a two-level tree:\\
        !           519: a root with no data unit but with zero or more children;
        !           520: and,
        !           521: each child has a data unit but no children
        !           522: 
        !           523: data unit is identified based on position in the file (relation to siblings)
        !           524: 
        !           525: insertions occur at end of file
        !           526: 
        !           527: erase at root node to empty file
        !           528: 
        !           529: ordered-flat differs by naming each child and identifying data units based
        !           530: on the name
        !           531: \end{note}
        !           532: 
        !           533: 
        !           534: \begin{bwslide}
        !           535: \ctitle        {EXAMPLE: GENERAL HIERARCHICAL CONSTRAINT SET}
        !           536: 
        !           537: \vskip.5in
        !           538: \diagram[p]{figure4}
        !           539: \end{bwslide}
        !           540: 
        !           541: 
        !           542: \begin{note}\em
        !           543: hierarchical: a tree of arbitrary structure
        !           544: 
        !           545: at a given level, nodes have the same ``type'' of name
        !           546: 
        !           547: insert as sister (sibling):\\
        !           548: the data unit becomes the next child visited when using preorder traversal
        !           549: (not valid for the root node, obviously)
        !           550: 
        !           551: insert as child:\\
        !           552: the data unit becomes the first child visited when using preorder traversal
        !           553: 
        !           554: note difference between fadu and data(du)
        !           555: \end{note}
        !           556: 
        !           557: 
        !           558: \begin{bwoverlay}
        !           559: \ctitle        {EXAMPLE: GENERAL HIERARCHICAL CONSTRAINT SET}
        !           560: 
        !           561: \vskip.5in
        !           562: \diagram[p]{figure4a}
        !           563: \end{bwoverlay}
        !           564: 
        !           565: 
        !           566: \begin{bwoverlay}
        !           567: \ctitle        {EXAMPLE: GENERAL HIERARCHICAL CONSTRAINT SET}
        !           568: 
        !           569: \vskip.5in
        !           570: \diagram[p]{figure4b}
        !           571: \end{bwoverlay}
        !           572: 
        !           573: 
        !           574: \begin{bwoverlay}
        !           575: \ctitle        {EXAMPLE: GENERAL HIERARCHICAL CONSTRAINT SET}
        !           576: 
        !           577: \vskip.5in
        !           578: \diagram[p]{figure4c}
        !           579: \end{bwoverlay}
        !           580: 
        !           581: 
        !           582: \begin{bwslide}
        !           583: \ctitle        {PRESENTATION STRUCTURE}
        !           584: 
        !           585: \begin{nrtc}
        !           586: \item  STRUCTURE OF EACH DATA UNIT IS DEFINED USING ABSTRACT SYNTAX NOTATION
        !           587:        ONE (ASN.1)
        !           588: 
        !           589: \item  SPECIFICATION CAN BE SIMPLE, e.g., A STRING OF OCTETS
        !           590: 
        !           591: \item  OR COMPLEX, e.g., A PERSONNEL RECORD
        !           592: \end{nrtc}
        !           593: \end{bwslide}
        !           594: 
        !           595: 
        !           596: \begin{bwslide}
        !           597: \ctitle        {TRANSFER STRUCTURE}
        !           598: 
        !           599: \begin{nrtc}
        !           600: \item  DATA UNITS ARE COMPOSED OF ``DATA ELEMENTS''
        !           601: 
        !           602: \item  EACH DATA ELEMENT MAPS DIRECTLY TO A ``WRITE'' TO THE NETWORK
        !           603: 
        !           604: \item  A TRANSFER STRUCTURE IS SAID TO BE ``SELF-DELIMITING'' IF EACH
        !           605:        DATA UNIT MAPS TO EXACTLY ONE DATA ELEMENT
        !           606: 
        !           607: \item  OTHERWISE, A 1:n RATIO IS USED AS AN EFFICIENCY ``HACK''
        !           608:     \begin{nrtc}
        !           609:     \item      DATA ELEMENTS ARE CONCATENATED TO FORM A SINGLE DATA UNIT
        !           610:     \end{nrtc}
        !           611: \end{nrtc}
        !           612: \end{bwslide}
        !           613: 
        !           614: 
        !           615: \begin{bwslide}
        !           616: \ctitle        {IDENTIFICATION STRUCTURE}
        !           617: 
        !           618: \begin{nrtc}
        !           619: \item  ACCESS CONTEXT:
        !           620:        AN ALGORITHM FOR DEFINING A ASPECT OF THE FILE STRUCTURE
        !           621: 
        !           622: \item  ACTIONS TAKEN IN THE CONTEXT OF THE CURRENT POSITION\\ (i.e., NODE)
        !           623: 
        !           624: \item  RECURSIVE ACTIONS PERFORMED IN PREORDER TRAVERSAL
        !           625: 
        !           626: \item  IMPORTANT DISTINCTION
        !           627:     \begin{nrtc}
        !           628:     \item      ALL DATA UNITS~---~THE NODE'S DATA UNIT AND DATA BELONGING
        !           629:                TO ALL CHILDREN OF THE NODE
        !           630: 
        !           631:     \item      SINGLE DATA UNIT~---~THE NODE'S DATA UNIT (IGNORE CHILDREN)
        !           632:     \end{nrtc}
        !           633: 
        !           634: \item  SEVERAL DEFINED (OF COURSE)
        !           635: \end{nrtc}
        !           636: \end{bwslide}
        !           637: 
        !           638: 
        !           639: \begin{bwslide}
        !           640: \ctitle        {EXAMPLE: ACCESS CONTEXTS}
        !           641: 
        !           642: \vskip.5in
        !           643: \diagram[p]{figure4}
        !           644: \end{bwslide}
        !           645: 
        !           646: 
        !           647: \begin{note}\em
        !           648: unstructured single data unit (US):\\
        !           649: transmit the node's data
        !           650: 
        !           651: unstructured all data units (UA):\\
        !           652: transmit all data in the fadu
        !           653: 
        !           654: flat single data unit (FS):\\
        !           655: transmit the single node's name and all data in the fadu
        !           656: 
        !           657: flat one level data units (FL):\\
        !           658: transmit names/data from all nodes at a given level having data
        !           659: 
        !           660: flat all data units (FA):\\
        !           661: transmit names/data from all nodes having data
        !           662: 
        !           663: hierarchical no data units (HN):\\
        !           664: transmit name, data, and structure
        !           665: 
        !           666: hierarchical all data units (HA):\\
        !           667: transmit name, data, and structure
        !           668: \end{note}
        !           669: 
        !           670: 
        !           671: \begin{bwslide}
        !           672: \part* {SUMMARY}\bf
        !           673: 
        !           674: \begin{nrtc}
        !           675: \item  THE VIRTUAL FILESTORE IS THE OPEN SYSTEMS ABSTRACTION OF A LOCALSTORE
        !           676: 
        !           677: \item  FILES CONTAIN ATTRIBUTES AND STRUCTURING INFORMATION IN ADDITION TO
        !           678:        ``TYPED'' DATA
        !           679: 
        !           680: \item  FILES ARE DISTINGUISHED BY NAME
        !           681: 
        !           682: \item  SOME ATTRIBUTES ARE DYNAMIC, ON A PER-CLIENT BASIS
        !           683: 
        !           684: \item  STRUCTURE IS BASED ON A HIERARCHICAL MODEL
        !           685: 
        !           686: \item  DATA AND STRUCTURE ARE SEPARATE AND DISTINCT
        !           687: 
        !           688: \item  DOCUMENT TYPES PROVIDE AN ABBREVIATED METHOD FOR REFERRING TO THE
        !           689:        FILE STRUCTURE
        !           690: \end{nrtc}
        !           691: \end{bwslide}

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