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Patterns, Frameworks, & Middleware: Their Synergistic Relationships Douglas C. Schmidt d. schmidt@vanderbilt. edu Professor Patterns, Frameworks, & Middleware: Their Synergistic Relationships Douglas C. Schmidt d. [email protected] edu Professor of EECS Vanderbilt University Nashville, Tennessee

Technology Trends (1/3) Information technology is being commoditized • i. e. , hardware & Technology Trends (1/3) Information technology is being commoditized • i. e. , hardware & software getting cheaper, faster, & (generally) better at a fairly predictable rate These advances stem largely from standard hardware & software APIs & protocols, e. g. : • Intel x 86 & Power PC chipsets • TCP/IP, GSM, Link 16 • POSIX, Windows, & VMs • Middleware & component models 2 • Quality of service (Qo. S) aspects

Technology Trends (2/3) Growing acceptance of a network-centric component paradigm • i. e. , Technology Trends (2/3) Growing acceptance of a network-centric component paradigm • i. e. , distributed applications with a range of Qo. S needs are constructed by integrating components & frameworks via various communication mechanisms Avionics Mission Computing Process Automation Quality Control Hot Rolling Mills Electronic Medical Imaging Software Defined Radio 3 Modalities e. g. , MRI, CT, CR, Ultrasound, etc.

Technology Trends (3/3) Component middleware is maturing & becoming pervasive … … Container Middleware Technology Trends (3/3) Component middleware is maturing & becoming pervasive … … Container Middleware Bus Replication 4 A/V Streaming Security Persistence Scheduling Notification Load Balancing • Components encapsulate application “business” logic • Components interact via ports • Provided interfaces, e. g. , facets • Required connection points, e. g. , receptacles • Event sinks & sources • Attributes • Containers provide execution environment for components with common operating requirements • Components/containers can also • Communicate via a middleware bus and • Reuse common middleware services

The Evolution of Middleware Applications Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure The Evolution of Middleware Applications Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware Operating Systems & Protocols Hardware 5 There are multiple COTS middleware layers & research/business opportunities Historically, mission-critical apps were built directly atop hardware & OS • Tedious, error-prone, & costly over lifecycles There are layers of middleware, just like there are layers of networking protocols Standards-based COTS middleware helps: • Control end-to-end resources & Qo. S • Leverage hardware & software technology advances • Evolve to new environments & requirements • Provide a wide array of reuseable, offthe-shelf developer-oriented services

Operating System & Protocols • Operating systems & protocols provide mechanisms to manage endsystem Operating System & Protocols • Operating systems & protocols provide mechanisms to manage endsystem resources, e. g. , • CPU scheduling & dispatching • Virtual memory management • Secondary storage, persistence, & file systems • Local & remove interprocess communication (IPC) • OS examples • UNIX/Linux, Windows, Vx. Works, QNX, etc. • Protocol examples • TCP, UDP, IP, SCTP, RTP, etc. INTERNETWORKING ARCH RTP TFTP MIDDLEWARE ARCH Middleware Applications HTTP TELNET DNS UDP Middleware Services TCP Middleware IP Solaris Fibre Channel Ethernet 6 ATM 20 th Century FDDI Win 2 K Vx. Works Linux Lynx. OS 21 st Century

Host Infrastructure Middleware • Host infrastructure middleware encapsulates & enhances native OS mechanisms to Host Infrastructure Middleware • Host infrastructure middleware encapsulates & enhances native OS mechanisms to create reusable network programming components • These components abstract away many tedious & error-prone aspects of low-level OS APIs • Examples • Java Virtual Machine (JVM), Common Language Runtime (CLR), ADAPTIVE Communication Environment (ACE) Asynchronous Event Handling Physical Memory Access Memory Management 7 Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware Asynchronous Transfer of Control Synchronization Scheduling www. rtj. org www. cs. wustl. edu/~schmidt/ACE. html

Distribution Middleware • Distribution middleware defines higher-level distributed programming models whose reusable APIs & Distribution Middleware • Distribution middleware defines higher-level distributed programming models whose reusable APIs & components automate & extend native OS capabilities • Examples • OMG CORBA, Sun’s Remote Method Invocation (RMI), Microsoft’s Distributed Component Object Model (DCOM) Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware • Distribution middleware avoids hard-coding client & server application dependencies on object location, language, OS, protocols, & hardware 8

Common Middleware Services • Common middleware services augment distribution middleware by defining higher-level domain-independent Common Middleware Services • Common middleware services augment distribution middleware by defining higher-level domain-independent services that focus on programming “business logic” • Examples • CORBA Component Model & Object Services, Sun’s J 2 EE, Microsoft’s. NET Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware • Common middleware services support many recurring distributed system capabilities, e. g. , • Transactional behavior • Authentication & authorization, • Database connection pooling & concurrency control • Active replication • Dynamic resource management 9

Domain-Specific Middleware • Domain-specific middleware services are tailored to the requirements of particular domains, Domain-Specific Middleware • Domain-specific middleware services are tailored to the requirements of particular domains, such as telecom, ecommerce, health care, process automation, or aerospace • Examples Siemens MED Syngo • Common software platform for distributed electronic medical systems • Used by all ~13 Siemens MED business units worldwide Boeing Bold Stroke • Common software platform for Boeing avionics mission computing systems 10 Modalities e. g. , MRI, CT, CR, Ultrasound, etc. Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware

Why We are Succeeding The past decade has yielded significant progress in Qo. S-enabled Why We are Succeeding The past decade has yielded significant progress in Qo. S-enabled middleware, stemming in large part from the following trends: • Years of iteration, refinement, & successful use Real-time CCM Web Services CORBA Component Model (CCM) Component Models (EJB) Real-time CORBA & DCOM DCE Micro-kernels RPC ARPAnet 1970 11 Year 2005 • The maturation of middleware standards Applications Domain-Specific Services Common Services Distribution Middleware Host Infrastructure Middleware Operating Systems & Protocols Hardware • NET, J 2 EE, CCM • Real-time CORBA • Real-time Java • SOAP & Web Services • The maturation of component middleware frameworks & patterns

Overview of Patterns • Present solutions to common software problems arising within a certain Overview of Patterns • Present solutions to common software problems arising within a certain context • Help resolve key software design forces • Capture recurring structures & dynamics among software participants to facilitate reuse of successful designs • Generally codify expert knowledge of design strategies, constraints & “best practices” Abstract. Service service Client Proxy service 12 1 1 Service service The Proxy Pattern • Flexibility • Extensibility • Dependability • Predictability • Scalability • Efficiency

Overview of Pattern Languages Motivation • Individual patterns & pattern catalogs are insufficient • Overview of Pattern Languages Motivation • Individual patterns & pattern catalogs are insufficient • Software modeling methods & tools largely just illustrate how – not why – systems are designed Benefits of Pattern Languages • Define a vocabulary for talking about software development problems • Provide a process for the orderly resolution of these problems • Help to generate & reuse software architectures 13

Taxonomy of Patterns & Idioms Type Description Examples Idioms Restricted to a particular language, Taxonomy of Patterns & Idioms Type Description Examples Idioms Restricted to a particular language, system, or tool Scoped locking Design patterns Capture the static & dynamic roles & relationships in solutions that occur repeatedly Active Object, Bridge, Proxy, Wrapper Façade, & Visitor Architectural patterns Express a fundamental structural organization for software systems that provide a set of predefined subsystems, specify their relationships, & include the rules and guidelines for organizing the relationships between them Half-Sync/Half. Async, Layers, Proactor, Publisher. Subscriber, & Reactor Optimization principle patterns Document rules for avoiding common design & implementation mistakes that degrade performance Optimize for common case, pass information between layers 14

Example: Boeing Bold Stroke Nav Sensors Vehicle Mgmt Mission Computer Data Links Radar Weapon Example: Boeing Bold Stroke Nav Sensors Vehicle Mgmt Mission Computer Data Links Radar Weapon Management Bold Stroke Architecture Weapons Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware (CPU, Memory, I/O) • Avionics mission computing product-line architecture for Boeing military aircraft, e. g. , F-18 E/F, 15 E, Harrier, UCAV • DRE system with 100+ developers, 3, 000+ 15 software components, 3 -5 million lines of C++ code • Based on COTS hardware, networks, operating systems, & middleware • Used as Open Experimention Platform (OEP) for DARPA IXO PCES, Mo. BIES, SEC, MICA programs

Example: Boeing Bold Stroke Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware Example: Boeing Bold Stroke Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware (CPU, Memory, I/O) 16 COTS & Standards-based Middleware Infrastructure, OS, Network, & Hardware Platform • Real-time CORBA middleware services • Vx. Works operating system • VME, 1553, & Link 16 • Power. PC

Example: Boeing Bold Stroke Reusable Object-Oriented Application Domainspecific Middleware Framework • Configurable to variable Example: Boeing Bold Stroke Reusable Object-Oriented Application Domainspecific Middleware Framework • Configurable to variable infrastructure configurations • Supports systematic reuse of mission computing functionality Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware (CPU, Memory, I/O) 17

Example: Boeing Bold Stroke Product Line Component Model • Configurable for product-specific functionality & Example: Boeing Bold Stroke Product Line Component Model • Configurable for product-specific functionality & execution environment • Single component development policies • Standard component packaging mechanisms Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware (CPU, Memory, I/O) 18

Example: Boeing Bold Stroke Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware Example: Boeing Bold Stroke Mission Computing Services Middleware Infrastructure Operating System Networking Interfaces Hardware (CPU, Memory, I/O) Component Integration Model • Configurable for product-specific component assembly & deployment environments • Model-based component integration policies 19 Operator Real World Model Avionics Interfaces Infrastructure Services

Legacy Avionics Architectures Key System Characteristics • Hard & soft real-time deadlines • ~20 Legacy Avionics Architectures Key System Characteristics • Hard & soft real-time deadlines • ~20 -40 Hz • Low latency & jitter between boards • ~100 usecs • Periodic & aperiodic processing • Complex dependencies • Continuous platform upgrades Avionics Mission Computing Functions • Weapons targeting systems (WTS) • Airframe & navigation (Nav) • Sensor control (GPS, IFF, FLIR) • Heads-up display (HUD) • Auto-pilot (AP) Board 1 1553 VME Board 2 20 4: Mission functions perform avionics operations 3: Sensor proxies process data & pass to missions functions 2: I/O via interrupts 1: Sensors generate data

Legacy Avionics Architectures Key System Characteristics • Hard & soft real-time deadlines • ~20 Legacy Avionics Architectures Key System Characteristics • Hard & soft real-time deadlines • ~20 -40 Hz • Low latency & jitter between boards • ~100 usecs • Periodic & aperiodic processing • Complex dependencies • Continuous platform upgrades Limitations with Legacy Avionics Architectures • Stovepiped • Proprietary • Expensive • Vulnerable • Tightly coupled • Hard to schedule • Brittle & non-adaptive 21 Nav Air Frame WTS AP FLIR GPS IFF Cyclic Exec 4: Mission functions perform avionics operations 3: Sensor proxies process data & pass to missions functions 2: I/O via interrupts Board 1 1553 VME Board 2 1: Sensors generate data

Decoupling Avionics Components Context Problems Solution • I/O driven DRE • Tightly coupled • Decoupling Avionics Components Context Problems Solution • I/O driven DRE • Tightly coupled • Apply the Publisher- application components • Complex Subscriber architectural pattern to distribute periodic, I/O-driven data from a single point of source to a collection of consumers • Hard to schedule dependencies • Expensive to evolve • Real-time constraints Structure Publisher produce Event Channel attach. Publisher detach. Publisher attach. Subscriber detach. Subscriber push. Event creates * Event Dynamics Subscriber consume : Event Channel : Subscriber attach. Subscriber produce : Event push. Event event receives consume Filter filter. Event 22 : Publisher detach. Subscriber

Applying the Publisher-Subscriber Pattern to Bold Stroke uses the Publisher. Subscriber pattern to decouple Applying the Publisher-Subscriber Pattern to Bold Stroke uses the Publisher. Subscriber pattern to decouple sensor processing from mission computing operations • Anonymous publisher & subscriber relationships • Group communication • Asynchrony Considerations for implementing the Publisher-Subscriber pattern for mission computing applications include: • Event notification model • Push control vs. pull data interactions • Scheduling & synchronization strategies • e. g. , priority-based dispatching & preemption • Event dependency management • e. g. , filtering & correlation mechanisms 23 Subscribers HUD WTS Air Frame Nav 4: Event Channel pushes events to subscribers(s) push(event) Event Channel push(event) GPS IFF 5: Subscribers perform avionics operations FLIR Publishers 3: Sensor publishers push events to event channel 2: I/O via interrupts Board 1 1553 VME Board 2 1: Sensors generate data

Ensuring Platform-neutral & Networktransparent Communication Context Problems Solution • Mission computing requires remote IPC Ensuring Platform-neutral & Networktransparent Communication Context Problems Solution • Mission computing requires remote IPC • Applications need capabilities to: • Support remote communication • Provide location transparency • Handle faults • Stringent DRE • Manage end-to-end Qo. S requirements • Encapsulate low-level system details • Apply the Broker architectural pattern to provide platform-neutral communication between mission computing boards Server Proxy Client Proxy marshal unmarhal receive_result service_p * calls 1 Client call_service_p start_task 24 Structure * 1 Broker message main_loop exchange srv_registration srv_lookup xmit_message manage_Qo. S 1 * message exchange marshal unmarshal dispatch receive_request * calls 1 Server start_up main_loop service_i

Ensuring Platform-neutral & Networktransparent Communication Context Problems Solution • Mission computing requires remote IPC Ensuring Platform-neutral & Networktransparent Communication Context Problems Solution • Mission computing requires remote IPC • Applications need capabilities to: • Support remote communication • Provide location transparency • Handle faults • Stringent DRE • Manage end-to-end Qo. S requirements • Encapsulate low-level system details : Client Proxy operation (params) : Broker : Server Proxy : Server register_service connect marshal Dynamics assigned port send_request unmarshal dispatch operation (params) receive_reply 25 • Apply the Broker architectural pattern to provide platform-neutral communication between mission computing boards result unmarshal result marshal start_up

Applying the Broker Pattern to Bold Stroke uses the Broker pattern to shield distributed Applying the Broker Pattern to Bold Stroke uses the Broker pattern to shield distributed applications from environment heterogeneity, e. g. , Subscribers HUD Air Frame push(event) • Programming languages • Operating systems • Networking protocols • Hardware A key consideration for implementing the Broker pattern for mission computing applications is Qo. S support WTS Nav Event Channel push(event) GPS IFF FLIR Publishers Broker • e. g. , latency, jitter, priority preservation, dependability, security, etc. 2: I/O via interrupts Board 1 Caveat These patterns are very useful, but having to implement them from scratch is tedious & error-prone!!! 26 6: Subscribers perform avionics operations 5: Event Channel pushes events to subscribers(s) 4: Sensor publishers push events to event channel 3: Broker handles I/O via upcalls 1553 VME Board 2 1: Sensors generate data

Overview of Frameworks Framework Characteristics • Frameworks provide • Frameworks exhibit • Frameworks are Overview of Frameworks Framework Characteristics • Frameworks provide • Frameworks exhibit • Frameworks are “inversion of control” at integrated domain-specific “semi-complete” structures & functionality runtime via callbacks applications Application-specific functionality Mission Computing Scientific Visualization E-commerce GUI Networking 27 Database

Comparing Class Libraries, Frameworks, & Components Component Architecture Class Library Architecture APPLICATIONSPECIFIC FUNCTIONALITY LOCAL Comparing Class Libraries, Frameworks, & Components Component Architecture Class Library Architecture APPLICATIONSPECIFIC FUNCTIONALITY LOCAL INVOCATIONS ADTs Math Naming Events Files Strings GUI EVENT LOOP GLUE CODE Locks Logging IPC Middleware Bus A class is a unit of abstraction & implementation in an OO programming language A component is an encapsulation unit with one or more interfaces that provide clients with access to its services Framework Architecture ADTs Strings INVOKES Files Reactor Class Libraries CALLBACKS GUI Locks DATABASE A framework is an integrated set of classes that collaborate to produce a reusable 28 architecture for a family of applications Frameworks Components Micro-level NETWORKING APPLICATIONSPECIFIC FUNCTIONALITY Locking Meso-level Macro-level Stand-alone language entities “Semicomplete” applications Stand-alone composition entities Domainindependent Domainspecific Domain-specific or Domain-independent Borrow caller’s thread Inversion of control Borrow caller’s thread

Using Frameworks Effectively Observations • Frameworks are powerful, but hard to develop & use Using Frameworks Effectively Observations • Frameworks are powerful, but hard to develop & use effectively by application developers • It’s often better to use & customize COTS frameworks than to develop inhouse frameworks • Components are easier for application developers to use, but aren’t as powerful or flexible as frameworks Successful projects are therefore often organized using the “funnel” model 29

Overview of the ACE Frameworks Features Applicationspecific functionality Acceptor Connector Stream Component Configurator • Overview of the ACE Frameworks Features Applicationspecific functionality Acceptor Connector Stream Component Configurator • Open-source • 6+ integrated frameworks • 250, 000+ lines of C++ • 40+ person-years of effort • Ported to Windows, UNIX, & real-time operating systems • e. g. , Vx. Works, p. So. S, Lynx. OS, Chorus, QNX • Large user community Task Reactor Proactor www. cs. wustl. edu/~schmidt/ACE. html 30

The POSA 2 Pattern Language Pattern Benefits • Preserve crucial design information used by The POSA 2 Pattern Language Pattern Benefits • Preserve crucial design information used by applications & middleware frameworks & components • Facilitate reuse of proven software designs & architectures • Guide design choices for application developers 31

Implementing the Broker Pattern for Bold Stroke Avionics Client Propagation & Server Declared Priority Implementing the Broker Pattern for Bold Stroke Avionics Client Propagation & Server Declared Priority Models Static Scheduling Service Standard Synchonizers Request Buffering Explicit Binding Thread Pools Portable Priorities Protocol Properties www. omg. org 32 • CORBA is a distribution middleware standard • Real-time CORBA adds Qo. S to classic CORBA to control: 1. Processor Resources 2. Communication Resources 3. Memory Resources • These capabilities address some (but by no means all) important DRE application development & Qo. Senforcement challenges

Applying Patterns & Framworks to Middleware: The ACE ORB (TAO) www. cs. wustl. edu/~schmidt/TAO. Applying Patterns & Framworks to Middleware: The ACE ORB (TAO) www. cs. wustl. edu/~schmidt/TAO. html 33 • TAO is an opensource version of Real-time CORBA • TAO Synopsis • > 1, 000 SLOC • 80+ person years of effort • Pioneered R&D on DRE middleware design, patterns, frameworks, & optimizations • TAO is basis for many middleware R&D efforts • Example of good synergy between researchers & practitioners

Key Patterns Used in TAO www. cs. wustl. edu/~schmidt/PDF/ORB-patterns. pdf 34 • Wrapper facades Key Patterns Used in TAO www. cs. wustl. edu/~schmidt/PDF/ORB-patterns. pdf 34 • Wrapper facades enhance portability • Proxies & adapters simplify client & server applications, respectively • Component Configurator dynamically configures Factories • Factories produce Strategies • Strategies implement interchangeable policies • Concurrency strategies use Reactor & Leader/Followers • Acceptor-Connector decouples connection management from request processing • Managers optimize request demultiplexing

Enhancing ORB Flexibility w/the Strategy Pattern Context Problem Solution • Multi-domain • Flexible ORBs Enhancing ORB Flexibility w/the Strategy Pattern Context Problem Solution • Multi-domain • Flexible ORBs must support multiple • Apply the Strategy pattern resuable event & request demuxing, scheduling, to factory out similarity middleware (de)marshaling, connection mgmt, amongst alternative ORB framework request transfer, & concurrency policies algorithms & policies Hook for marshaling strategy Hook for the event demuxing strategy Hook for the connection management strategy Hook for the request demuxing strategy Hook for the concurrency strategy Hook for the underlying transport strategy 35

Consolidating Strategies with the Abstract Factory Pattern Context Problem Solution • A heavily strategized Consolidating Strategies with the Abstract Factory Pattern Context Problem Solution • A heavily strategized framework or application • Aggressive use of Strategy pattern creates a configuration nightmare • Apply the Abstract Factory pattern to consolidate multiple ORB strategies into semantically compatible configurations • Managing many individual strategies is hard • It’s hard to ensure that groups of semantically compatible strategies are configured Concrete factories create groups of strategies 36

Dynamically Configuring Factories w/the Component Configurator Pattern Context Problem Solution • Resource • Prematurely Dynamically Configuring Factories w/the Component Configurator Pattern Context Problem Solution • Resource • Prematurely commiting to a particular ORB • Apply the Component constrained configuration is inflexible & inefficient Configurator pattern & highly to assemble the • Certain decisions can’t be made until dynamic desired ORB factories runtime environments (& thus strategies) • Forcing users to pay for components dynamically that don’t use is undesirable • ORB strategies are decoupled from when the strategy implementations are configured into an ORB • This pattern can reduce the memory footprint of an ORB 37

ACE Frameworks Used in TAO • Reactor drives the ORB event loop • Implements ACE Frameworks Used in TAO • Reactor drives the ORB event loop • Implements the Reactor & Leader/Followers patterns • Acceptor-Connector decouples passive/active connection roles from GIOP request processing • Implements the Acceptor. Connector & Strategy patterns • Service Configurator dynamically configures ORB strategies • Implements the Component Configurator & Abstract Factory patterns 38

Summary of Pattern, Framework, & Middleware Synergies The technologies codify expertise of experienced researchers Summary of Pattern, Framework, & Middleware Synergies The technologies codify expertise of experienced researchers & developers • Frameworks codify expertise in the form of reusable algorithms, component implementations, & extensible architectures Application-specific functionality Acceptor Connecto r • Patterns codify expertise in • Middleware codifies the form of reusable expertise in the form of architecture design themes & standard interfaces & styles, which can be reused components that provide event when algorithms, applications with a simpler components implementations, façade to access the or frameworks cannot powerful (& complex) capabilities of frameworks Stream Component Configurator Task Reactor Proactor There are now powerful feedback loops advancing these technologies 39

The Road Ahead (1/2) Key Challenges CORBA Apps CORBA Services CORBA J 2 EE The Road Ahead (1/2) Key Challenges CORBA Apps CORBA Services CORBA J 2 EE DRE Applications Apps Middleware J 2 EE Services Middleware J 2 EE . NET Apps . NET Services . NET • There is a limit to how much application functionality can be factored into broadly reusable standard COTS middleware • Middleware has become extremely complicated to use, configure, & provision statically & dynamically Load Balancer FT CORBA Workload & Replicas RT/DP CORBA + DRTSJ Hardware & Networks 40 RTOS + RT Java CPU & memory Int. Serv + Diffserv Operating Sys & Protocols Connections & priority bands Network latency & bandwidth • There are now (& will always be) multiple middleware technologies to choose from

The Road Ahead (2/2) Solution approach: Integrate model-based software technologies with Qo. S-enabled component The Road Ahead (2/2) Solution approach: Integrate model-based software technologies with Qo. S-enabled component middleware … … Container Qo. S-enabled Middleware Bus <…> <…> <…events this component supplies…> 41 … … • e. g. , standard technologies are emerging that can: 1. Model 2. Analyze 3. Synthesize & 4. Provision multiple layers of Qo. S-enabled middleware • These technologies are guided by patterns & implemented by component frameworks Container Distributed system

Concluding Remarks R&D Synergies • Researchers & developers of distributed systems face common challenges, Concluding Remarks R&D Synergies • Researchers & developers of distributed systems face common challenges, e. g. : • connection management • service initialization • error handling • flow & congestion control • event demultiplexing • distribution • concurrency & synchronization • fault tolerance • scheduling & • persistence • Pattern languages, frameworks, & component middleware work together to help resolve these challenges Key open R&D challenges include: • Prior R&D efforts have address some, but by no means all, of the challenging DOC middleware research topics 42 • Layered Qo. S specification & • Multi-level global enforcement resource mgmt. & • Separating policies & optimization mechanisms across layers • High confidence • Time/space optimizations for • Stable & robust middleware & apps adaptive systems

Additional Information • Patterns & frameworks for concurrent & networked objects • www. cs. Additional Information • Patterns & frameworks for concurrent & networked objects • www. cs. wustl. edu/~schmidt/POSA/ • www. cs. wustl. edu/~schmidt/ACE/ • ACE & TAO open-source middleware • www. cs. wustl. edu/~schmidt/ACE. html • www. cs. wustl. edu/~schmidt/TAO. html • Research papers • www. cs. wustl. edu/~schmidt/research. html • Tutorial on patterns, frameworks, & middleware • UCLA extension, July 9 -11, 2003 • www. cs. wustl. edu/~schmidt/UCLA. html • Conferences on patterns, frameworks, & middleware 43 • DOA, ECOOP, ICDCS, ICSE, Middleware, OOPSLA, PLo. P(s), RTAS,