John R Durrett1 Client/Server Computing Byte April 1995 & The Martian C/S book

John R Durrett2 Is C/S a passing fad? u Mainframe era –the “right” hardware vendor –software, front-end, apps, etc u The PC & C/S revolution –“Open systems” –mix-and-match F c & s platform F network protocols F DCE infrastructure F etc. u Good: liberating, low-cost, flexibility u Bad: much harder to manage

John R Durrett3 Change u Old: –Servers are scarce –LANs –Clearly segregated services u New: –Servers are plentiful –Proximity does not matter –OOUI F Integrates multiple concurrent processes F Interaction

John R Durrett4 Client/Server visions u The death of mainframes u Mainframes reborn u Peace: middle ground u MIS shops in the new era –much harder to manage –requires much more variety in skills –distributing MIS functions to users?

John R Durrett5 What is C/S u Service provider & consumer –Clients always initiate –encapsulation of services u Shared resources u Location transparency –continual flux –global u Namespace transparency –unique resolution –dynamic

John R Durrett6 Network Operating System u Administrative transparency –Synchronization, network failures, etc. u Secured-access transparency –Mutual distrust –ID verification –Access control lists u Communications transparency –Heterogeneous data –Message oriented middleware

John R Durrett7 Applications u Planetary electronic mall u Technologies –Rich transaction processing –Roaming agents –Rich documents

John R Durrett8 Client/Server models u File servers u SQL databases –transaction servers u TP monitors u Groupware u Distributed objects

John R Durrett9 SQL u Dominate today u Well known language u Stored procedures u Extensions –triggers –rules u Non-standard progress –LCD is SQL

John R Durrett10 TP Monitors u Manage processes u Transaction oriented u Contract u Fundamental unit –recovery –consistency –concurrency u Flat model u Sub-transaction model u Overkill for small LANs u Scales well to large networks

John R Durrett11 Groupware u Multimedia u Document management u Unstructured data u u Work flow processing –sequential routes –parallel routes –feedback –acceptance criteria

John R Durrett12 Distributed Objects u Encapsulates data & business logic u Wrappers for legacy apps u Most standardized u Interface Definition Language u Can subsume all other forms of C/S

John R Durrett13 Distribution of applications u Fat clients –traditional model –file server –database server u Fat servers –minimize network load –transaction servers –object servers

John R Durrett14 C/S Building Blocks u architecture –structural details –by computers not plans –c/s questions F split F scalability F mobile - home u New demographics –single machine –single server –multi-server –distributed objects

John R Durrett15 Infrastructure u client u server u middleware –transport stacks F O/S interface –NOS F extends local O/S F single system illusion F app coordination –ORB F services F location transparent connectivity