Meta-Programming middleware for distributed object computing 2003 Peter Breitling Fakultät für Informatik Technische Universität München

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 introduction : the vision of the web of objects Marc Andreesen, netscape Cofounder (1996) The internet as a web of software objects where –software is composed of and references distributed web objects, –the objects are loaded dynamically on client or leave on server, –we „use“ our set of applications seamlessly on any computer... is still a vision. Instead: –software uses existing libraries by copy-and-paste. –web objects are mainly used as services –we manually „download an use“ our set of applications on each computer with application specific update mechanisms. „We expect that over the next few years IIOP will become as ubiquitous as HTTP and CGI“

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Internet as a web of objects  Benifits in contrast to local applications include: –Location independent personal environment and profile –Data security: Background backup, replication to server –Interoperable update mechanisms on component level –Basis for „Application Service Providing“ Additional requirements for local web applications: –Provider concept: Each software object has a known origin –Offline capabilities: Software can work (sometimes partially) offline –Security: The software should run in a sandbox –Privacy: controllable access to personal data and profile

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Possible approaches Different possible approaches to the problem  define yet another component system.  extend an existing doc middleware with more manageable location service and implementation replication.  define a middleware layer where existing technologies can be adapted to and extended services can be implemented on top.

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Different possible approaches to the problem  define yet another component system.  extend an existing doc middleware with more manageable location service and implementation replication.  define a middleware layer where existing technologies can be adapted to and extended service can be implemented on top. Possible approaches

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 introduction: meta-programming What is Meta-Programming: –Literally: programming where programms are data –In context of doc: dynamic software generation, mapping and reuse Meta-Programming application domains: –Adaption and monitoring –Packaging and distribution –Installation and reconfiguration Well known Meta-Programming examples: –compiler, debugger, profiler, interpreter On the programming level (and often compared for doc in literature): –pluggable protocols, interceptors, smart proxies Mostly handwork and application specific!

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 introduction: technology dependency Dependency of specific technology for software devolopment phases Requirements Elicitation Specification Design Implementation Integration Maintenance / Adaption / Reuse weak dependency strong dependency

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Metadoc prototype: a meta-middleware Observation: ► Meta-Programming features are strongly technology dependent Approach with Metadoc: ► Find an abstract and technology-independent model for Meta- Programming in the context of doc that –provides standardized interoperable mechanisms –focuses on object generation, mapping and reuse

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 approach: find common, abstract model Classic elements of doc-computing –Entities: object-interfaces, -implementations, -instances –Object registry, location and activation mechanisms –Access-references (RPC) between object instances through protocols... are not enough for management for deployment and reuse since: –Existing environment dependencies (e.g. of next tier, database, filesystem) –Missing mechanisms and meta-information for deployment and update like origin and usage Thus a special abstract model is introduced for meta-middleware with –software components as resources –Component context as environments

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15  Extended oo-view with 4 fundamental resource classes –type: dependent of the resource class binary: mime-type document: document-type implementation, instance: document res.-ref. of type interface –state: subset of serializable, registered, persistent, published, versioned –attributes: (name, value) set, extendable and managed by value –(registry, name): registry reference and name in registry if registered name unique in registry, registry identifier globally unique The doc resource model for meta-programming  Resources are 5 tupels: Resource (type, class, state, attributes, registry) instanceimplementationdocumentbinary

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 example: resource type transformations Resource Binary Document Implementation Instance cast serialize new

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Metadoc: Reference implementation in Java Environment connectors Environment configuration Framework implementation Framework API Resource resolver IIOP, HTTP / WebDAV, WSDL / SOAP UI, XML, (API) Java,.Net, Corba OO, procedural, scripting IIOP, HTTP, WSDL / SOAP Prop. IEP P2P, Client Server

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 Prototype configuration UI Accessible by existing web- technologies Environment configuration Access to existing web-technologies Environment Framework implementation

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 an abstracted view on existing technologies  Filesystems as Binary Registries  Binary resource remote access through NFS, SMB, FTP, HTTP, WebDAV,...  XML-Databases as Document Registries  Corba Interface Repository as a Document Registry of class Interface  Corba Services, UDDI as Instance Registries  Instance resource remote access through RPC, IIOP, RMI, SOAP...  Corba Implementation Repositories as Implementation Registries  Locating / Trading implementations with local instanciatiation not standardised in existing doc-middleware though it is a central functionality for a web-of-objects.

Meta-Programming middleware for distributed object computing, Peter Breitling, DAIS / 15 summary and future work  Interoperable specification for access on distributed resources –Integrated management and access to binaries, documents and object implementation and instances. –Mappable in different ways to existing middleware technologies –Capable for implementing sophisticated deployment and reuse methods. –Methods for security (mostly), persistency, transactions on application level  Prototype in Java, supported protocols: –HTTP / WebDAV: binary, document and implementation connectors and resolver –IIOP: Interface and instance environment and resolver –EJB,.Net: Interface and Instance resolver (not in first release) –IEP: Inter-environment configuration and resolver protocol ► Project homepage and up-to-date information: please register for notification about first release (thank you).