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Designing Distributed Object Systems

Designing Distributed Object Systems. Ian Gorton, Paul Greenfield Advanced Distributed Software Arhitectures and Technologies CSIRO, Sydney. Who is CMIS?. CSIRO is Australia’s largest scientific R&D organisation and has around 7000 staff CSIRO Mathematical and Information Sciences is

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Designing Distributed Object Systems

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  1. Designing Distributed Object Systems Ian Gorton, Paul Greenfield Advanced Distributed Software Arhitectures and Technologies CSIRO, Sydney

  2. Who is CMIS? • CSIRO is Australia’s largest scientific R&D organisation and has around 7000 staff • CSIRO Mathematical and Information Sciences is • Australia’s premier group of mathematicians and Information Technology specialists working to improve performance in Australian industry.

  3. ADSaT • 11 person R&D group, Sydney and Canberra • Involved in software engineering R&D • Specifically looking at the problems of distributed systems, eg • architecture, components, technologies • testing and analysis • performance, scalability, reliability

  4. Architecture Issues Physical constraints Security Transactions Management Solution Space Fault Tolerance Technologies, Components Performance Requirements/Scalability Testing Trade-offs between competing forces can be extremely complex

  5. ADSaT capabilities • Designing software architectures • Expertise in enterprise distributed technologies (eg COM, ORBs, DCE, Java), transactions, databases • Research based around software architectures • In-depth knowledge of Internet and e-commerce issues

  6. Week1 Distributed Systems Technology Overview Acronym frenzy!!

  7. What is Middleware? Software plumbing and associated services for building distributed systems

  8. Basic distributed systems blocks The Next Big Thing?? • Provides high(ish) level facilities (RPC, RMI) for building distributed system communication infrastructures • Hides low level issues from the programmer through abstraction Component Technologies CORBA/RMI/COM TCP/IP Network/OS

  9. Associated Services Security Transactions Directory Messaging • Basic middleware add-ons • Fulfill common application needs in distributed systems • See CORBA Services spec for an example and comprehensive list Middleware Plumbing

  10. Middleware Technologies • CORBA • COM • Java • DCE • Proprietary, ie • Forte, Tuxedo, CICS, etc.. • TIBCO, MQ, etc..

  11. So What is it Good For? • Geek answer… • Middleware makes it feasible ‘for mere mortals’ to build distributed software systems that are: • high-performance, scalable • reliable, high availability • Don’t be fooled. Distributed systems are inherently difficult to build.

  12. Er..try me again? • The bottom line answer... • Businesses need a WWW presence • secure, transactional accesses to business systems • Integration • mergers, acquisitions, virtual enterprises • Internet competition and time-to-market

  13. Some Gartner Survey Figures • To develop a currently competetive e-commerce site: • 5 months average duration (some 1 year+) • uses more than 1 consulting organization • cost average US$1 million (~$350K-$2m+) • 79% costs were labor, 10% s/w • No enterprise WWW site was ‘on budget’

  14. Gartner Group Predictions • Simple site - $300k-$1 million • Competetive site - $1-5 million • Market leader - $5-20 million • Site costs will increase 25% annually in next few years

  15. Solving Business Problems with Middleware • Legacy system access • Data integrity • Scalability • Availability • Client access

  16. Legacy System Access AS400 CICS\VSAM • Ease legacy system integration by providing standard interfaces (wrappers) • Hides details of legacy systems from clients MQ CICS Gateway Server Server Middleware Wrappers Clients Clients

  17. Data Integrity Oracle SQL Server • Ensuring data integrity with distributed databases requires transactions • Transactions ensure ACID properties TP Service SQL ODBC Server Server Clients Clients

  18. Scalability • Middleware supports scaling system performance by service replication • This isn’t free - it requires good architecture! Server Server Clients Clients

  19. Availability • Replication enhances fault tolerance and improves availability • Graceful degradation, lower performance but it keeps running Server Server Clients Clients

  20. Client Access • Client access enhanced due to: • physical distribution • variety of access technologies (ie Internet protocols, IIOP, COM) and available bridges. Clients HTTP WWW Server Server IIOP COM Bridge IIOP Clients Clients

  21. Enterprise Middleware Products • Some terminology first: • Middleware - basic products • Orbix, Visibroker, DCE, Java RMI, COM • Object Transaction Monitor (OTM) • middleware plus enterprise systems capabilities, OrbixOTM, BEA WebLogic • Application Server • cynical answer - new name for OTMs with Java 2 Enterprise Edition support :-}

  22. N-Tier System Architecture Client layer (browser, applets, apps) http, IIOP, COM, RMI, XML WWW server (WWW server, JSPs, ASPs) Security IIOP, COM, RMI, XML Transactions Business Logic (CORBA objects, EJBs, COM+) SQL, ODBC, JDBC, XA Data Access (DBMSs)

  23. Standards (wot standards?) • CORBA - OMG • Java 2 Enterprise Edition (EJB+JMS+JNDI+…) - Sun • COM+ - Microsoft • MQ Series - IBM • TIBCO multicast protocol.. • ???

  24. CORBA • OMG is vendor consortium • CORBA Interface Definition Language (IDL) • Internet Inter-ORB Protocol (IIOP) (GIOP over TCP/IP) • CORBA services, eg transactions, naming, events, security

  25. Java • Remote Method Invocation (RMI) • Sun’s JRMP or RMI-over-IIOP • Enterprise Java Beans (EJBs) • Java Transaction Service (JTS) • Java mapping to CORBA OTS • Java Naming and Directory Interface (JNDI) • Java Messaging Service (JMS)

  26. EJBs • EJBs are server-side components • Separate business logic from infrastructure code EJB EJB EJB EJB Container

  27. EJBs • EJBs capture design patterns: • Stateless Session Bean • Stateful Session Bean • Entity Bean (bean or container managed) • Containers/EJB Servers provide: • transaction policies • security policies • database connection pooling • multi-threading

  28. Transaction Service • Essential for distributed transaction processing • Manages consistent updates to multiple databases • CORBA OTS, Java JTS, M’soft MTS • X/Open DTP standards - XA

  29. ACID properties • A set of operations that have ACID properties: • Atomic • Consistent • Isolated • Durable • Classic example - a bank account transfer

  30. Java Transaction Example try { // Create a transaction. transaction.begin(); // Invoke operations in transaction savingsAccount.makeWithdrawal(50) chequeAccount.makeDeposit(50); // Commit the transaction. transaction.commit(true); } catch (APP_ERROR ex) { transaction.rollback() } catch (TRANSACTION_ROLLEDBACK ex) { // handle rollback }

  31. Two-Phase Commit

  32. X/Open Distributed TP Reference Model

  33. XA Interface details • Database must implement an XA library compatible with transaction service product • embedded SQL • ODBC/DTC for SQL Server • OCI for Oracle • ??? Others... • JDBC-2 incorporates XA support • No XA - no distributed transactions

  34. Directory Service • Clients need to get references to server objects • Server objects advertise their reference in a directory service • Clients query the directory service to retrieve desired reference • CORBA Naming service, JNDI, LDAP

  35. Bank Stocks Loans Accounts BusLoan HomeLoan AccountService NewStock Service QueryStock Example Name Space

  36. Security • Provide: • user authentication • user/service authorization • encryption • Secure Socket Layer (SSL) • public key infrastructure • asymmetric private and public keys • X.509 digital certificates

  37. Messaging • Many apps require asynchronous communications • CORBA event/notifcation/messaging service • Java Messaging Service • TIBCO/Rendezvous • MQ Series • others… • More on these later...

  38. WWW Server Tier • Need to accept HTML requests via HTTP post or get • CGI scripts first used to add processing capability: • spawn new process for each request • slow, doesn’t scale • Proprietary improvents • Netscape’s NSAPI, Microsoft’s ISAPI

  39. Java Servlets/Server Pages • Java platforms includes specs for: • servlets • Java Server Pages (JSPs) • Java servlets launched by WWW Server in response to URL request • JSP’s allow code (eg Java beans) for formatting dynamic content to be embedded in HTML page

  40. Java Servlets/Server Pages invoke query URL JSP App. Server Component results html WWW Server invoke query Servlet HTML results html

  41. Extensible Markup Language (XML) • Subset of SGML • Standard textual format for structured documents • Document Type Definition (DTD) defines document structure with tags for each entry in the document • XML document instance contains both tags and document data • Text format is easy to process

  42. Sample DTD <?xml encoding="US-ASCII"?> <!ELEMENT orders (order)*> <!ELEMENT order (header,item+,total)> <!ELEMENT header (billing_info,shipping_info)> <!ELEMENT billing_info (name,address,credit_card)> <!ELEMENT shipping_info (name,address)> <!ELEMENT name (given,family)> <!ELEMENT address (street,city,state,zipcode,country,phone)> <!ELEMENT item (product_id,product_name,quantity,price)> <!ELEMENT credit_card (#PCDATA)> <!ELEMENT given (#PCDATA)> <!ELEMENT family (#PCDATA)> […ELEMENTS MISSING…..] <!ELEMENT product_id (#PCDATA)> <!ELEMENT product_name (#PCDATA)> <!ELEMENT quantity (#PCDATA)> <!ELEMENT price (#PCDATA)> <!ELEMENT total (#PCDATA)>

  43. Sample (Incomplete) XML Document <?xml version="1.0"?> <!DOCTYPE orders SYSTEM "orders.dtd"> <orders> <order> <header> <billing_info> <name> <given>John</given> <family>Doe</family> </name> <address> <street>555 Main Street</street> <city>Mill Valley</city> <state>California</state> <zipcode>94520</zipcode> <country>USA</country> <phone>707 555-1000</phone> </address>

  44. Extensible Style Language (XSL) • XML ignores presentation of data • XSL stylesheets define presentation of XML doc in some format XML Doc HTML, PDF, etc... Compiler XSL in browser or WWW server

  45. XML/XSL Impact • Major vendor support/momentum • Presentation • Decoupling content/presentation is good! • Presentation is the browser’s job • Data interchange • business-to-business e-commerce • DOM API - XML parsers produce a DOM representation of an XML document • Microsoft’s SOAP

  46. Summary • Distributed object system technology is a key part of building enterprise distributed systems • There’s a lot of : • design issues • technology issues • plain hard issues (ie testing) • This course is just the ‘entrée’...

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