Customer consulting and training at a computer retailer

Software: ARM-610 Risc-Assembler

Hardware: Acorn Archimedes Risc-Computer, Reparaturen PC-Kompatible

Client/end customer: Micro Computer Weber GmbH

Period: 1987

Porting "Giana Sisters" in coproduction

Software: Desktop application, Graphic programming, Game programming

Client/end customer: Escal Software GmbH

Period: 1988

Design and programming of a travel booking portal

Complex determination of suitable trips and total prices from given departure and arrival data.

Software: CSS, Database modeling, Html, JavaServer Pages JSP, Perl, PHP, Web application

Hardware: IBM-PC compatible

Client/end customer: Travix GmbH, DER-Tours GmbH

Period: 1992

Implementation of an archiving system

Complete development of a document archiving system, master/multi-slave architecture, scanner connection

Software: BTrieve database, Desktop application, Netware network programming, Visual Basic

Client/end customer: Wolf & Simonis GmbH

Period: 1995

Sensor evaluation for hot runner safety system

Multi-threads, quasi real-time, high error redundancy, multi-master, multi-slave

Software: C++, Visual C/C++

Client/end customer: SST GmbH, Deutsche Bahn AG

Period: Oct. 1997 – Apr. 1998

Racing car engine control prototyping

Rush order prototype construction including coordination of project management

Hardware: Analog Technology, Design of complex control systems, Electronics development, Circuit board layout

Client/end customer: Visteon AG, Ford Automotives AG

Period: Feb. 1998 – Mar. 1998

Contract development for a biometrics manufacturer Fingerprint

Hardware development PCI-card/sensor technology, real-time image driver.

Software: Ansi C, Image processing techniques, C++, Turbo Pascal

Hardware: Design von PCI-Karten, Electronics development

Client/end customer: Berg Data AG, Thomson CSF

Period: 03.06.1998 – 25.11.1999

Business Channel

Integration of the content management system "open market" to combine 5 websites (Börse-Online, Impulse, Finanzen, Capital, Bizz) into one large web portal "Business Cannel"

XML interface design and control for content delivery, data porting SQL, project documentation and partly coordination, consulting activity: technical/management

Software: Content management CMS, Documentation, Html, IPS/Openmarket, Java, JavaServer Faces JSF, JavaServer Pages JSP, Open Market Content Management, Perl, Interface specification, Web application, XML

Client/end customer: BFL GmbH, Mphasis Europe B.V., Gruner & Jahr AG

Period: 01.10.2000 – 31.12.2000

Freelancer intranet medical practice software/health card

Debugging of the entire software and implementation of a uniform system-wide printing concept.

Software: ASP, Desktop application, Html, MS-Sql, MS-Transaction Server

Client/end customer: med medicine online GmbH

Period: 01.05.2001 – 30.09.2001

Vehicle sales portal Nutzfahrzeugfinder.de

Agency portal (à la AutoScout24) for the sale of commercial vehicles of all kinds.

Flexible parameterized search engine, extensive database of all commercial vehicles, login area for vehicle suppliers, administration area

Software: Apache Web-Server, Image processing techniques, Content management CMS, Database modeling, Html, J2EE, Java, JDBC, JEE, Linux, Linux Administration, PHP, Postgres, Interface specification, Security, Tomcat, Web application, Web-Templating

Client/end customer: nutzfahrzeugfinder GmbH

Period: 23.05.2001 – 15.07.2002

EMail game content management system/access rights

ALWS specification and implementation

Software: Content management CMS, Database modeling, Document-Processing, Documentation, Java, JDBC, Interface specification, Web application

Client/end customer: BoST GmbH

Period: 19.09.2001 – 17.10.2001

Web based content management system

Realization of a web based content management system for the "learning workshop" with a flexible categorization of the articles and mapping of different categories on the page navigation.

Content management system developed on behalf of a customer, which optimally supports the freely graduated navigation of the traffic education portal Lernwerkstadt. The result was a thematically indexed filing of articles. The articles are delivered by cleverly combining several topics. The content-related categorization makes it possible to change or refine the navigation without any effort. A flexible description language for the delivery of the articles enables quick adjustments to the different designs or color spaces within the presence. These design templates are also maintained within content management. Java servlets and a Sql connection to Postgres and MS-Sql servers are used. The presence implemented by the customer calls up the article view and the right teaser area. These areas are delivered completely prepared.

Software: Content management CMS, Java, JavaCC, JavaScript JS, Java Servlets, JDBC, MS-Sql, Postgres, Web application

Client/end customer: BoST GmbH, Volkswagen AG, Klett Verlag GmbH, Deutsche Verkehrswacht e.V.

Period: 17.08.2002 – 13.09.2002

Co-development of a CRM system for industry and wholesale

Data connection and graphical user interfaces including complete networked appointment management with optically sophisticated calendar. Data export and printing of invoices through document processing via Postscript or PDF.

Software: Apache FOP, Desktop application, Document-Processing, J2EE, Java Swing, JEE, MySql, PDF, PostScript, SAP environment, XML-FO

Hardware: Scanner integration, Bar code

Client/end customer: ARM GmbH

Period: 02.06.2003 – 11.06.2004

Implementation CMS for the internet portal "Geldidee"

Complete restructuring and unbundling of the internet portal. Implemetation of the Typo3 content management system. Connecting external partners sites via Typo-Script.

Software: Content management CMS, Html, JavaScript JS, PHP, Rest, Typo3, Web application

Client/end customer: Bruno Media GmbH, Gruner & Jahr AG

Period: 01.07.2004

Development online photo book portal

Software: Java, Java Hibernate, JavaServer Pages JSP, Java Servlets, Java Spring, JBoss, PHP, Rest, Web application

Client/end customer: iplabs GmbH, CEWE Stiftung & Co. KGaA

Period: 01.03.2005 – 31.05.2005

Production control, connection to merchandise management

Software: PDF, XML

Client/end customer: Vondar IO Ltd.

Period: Oct. 2005 – 06.06.2006

Clexane trombose management programm

Software: Desktop application, Real Basic (structured)

Client/end customer: Academy GmbH, Sanofi Aventis GmbH

Period: 24.05.2006 – 29.11.2007

Realization of the internet portal Billig-Flieger-Vergleich.de

Implementation of the server-platform of a flight-price-comparison web-page. Accessing different datasources of the airlines and travel operators, consolidating and presenting for the user.

Parallel life queries of flight searches, consolidation of results (XML, CSV data), data handling and system administration. Support in the creation of the application and technical assistance in the operation of the popular portal: Cheap Flight Comparison. Here you will find a good overview of cheap flights and can compare all cheap airlines with each other.

Software: GWT, Html, JavaScript JS, JSON, Linux Administration, MySql, PHP, Web application

Client/end customer: Netzpool GmbH

Period: 13.07.2006 – 12.02.2009

Website "golf comparison"

Software: Content management CMS, PHP, Interface specification, Web application

Client/end customer: Metaflake GmbH

Period: 06.09.2006 – 22.12.2006

Avalox COPD-Tool

Software: Desktop application, Real Basic (structured)

Client/end customer: Academy GmbH

Period: 27.09.2006 – 27.06.2007

CSII-Expertise

Implementing medical diagnosis software (expert-systems), that supports doctors to choose the correct medication or technical equipment (COPD, CS-II, Hypertension).

Software: Desktop application, Real Basic (structured)

Client/end customer: Academy GmbH, Roche AG

Period: 26.01.2007 – 21.06.2007

Prevention Guide

Software: GWT, Java, Java Servlets, Web application, Web-Objects

Client/end customer: Academy GmbH

Period: 11.05.2007 – 10.12.2007

Hypertonie Documentation tool

Software: Desktop application, Real Basic (structured)

Client/end customer: Academy GmbH

Period: 31.05.2007 – 09.08.2007

Web based statistical system "Try And Play"

Software: GWT, Java, JavaServer Pages JSP, Java Servlets, JDBC, JSON, Oracle DB, Postgres, Web application, Weblogic

Client/end customer: Reality Bytes GmbH, Samsung Mobile AG

Period: 04.07.2007 – 07.02.2008

Coupling and single sign login of various components for the web-platform of "Young Woman’s Magazine"

Software: CSS, JavaServer Pages JSP, PHP, Rest, Sessiontracking, Web application

Client/end customer: Reality Bytes GmbH, Burda Media Publishing KG

Period: 31.07.2007 – 03.08.2007

CMS for dynamic generation of static pages

Software: Content management CMS, Java, JavaScript JS, web2obj, Web application, Web service, Web-Templating, XML

Client/end customer: Metaflake GmbH

Period: 10.01.2008

Consulting Vitaphone ISP2.0a - medication and MMI browser

Client/end customer: Star Healthcare Management GmbH, Vitaphone GmbH

Period: 14.11.2008 – 23.03.2009

Development of the "flying dinner" internet community

Software: CSS, Html, MySql, PHP, Web application

Client/end customer: Netzpool GmbH

Period: 15.11.2008 – 25.11.2008

Development "Queryserver"

Request flight data and fares from the various flight and travel providers. Official interfaces or allowed screen scraping if no export interfaces are available. Parallel life queries of flight searches, consolidation of results (XML, CSV data), data handling and system administration.

Software: Database modeling, Remote administration, Html, Java, Java NIO, JDBC, Linux, Linux Administration, MySql, ServerSockets, sFTP, Sockets, Web application, Web service, XML

Client/end customer: Netzpool GmbH

Period: 15.01.2009 – 12.02.2009

ICD/CRT Integration STAR Plus

Client/end customer: Star Healthcare Management GmbH

Period: 22.04.2009 – 22.06.2009

Print data personalization & PDF composition software

Realising a print data personalization software for transforming huge incoming travel-booking-reservations in different formats into complety assembled (composing/sorting) print jobs for producing booklets. Based on my PDF-composition-library from my photobook-prepress-server.

Software: Image processing techniques, Desktop application, Document-Processing, Prepress, DTP, iText, Java, Java Swing, JDBC, PDF, PDF-Templating, VIPP, web2obj, Web service, Web-Templating, XML

Hardware: Printing technology, Xerox Docucolor, Xerox IGEN

Client/end customer: Infox GmbH

Period: 01.06.2009 – 30.06.2017

Internet book price calculator for publisher/printing/bindery

Software: CSS, Html, JavaScript JS, JSON, PHP, Web application

Client/end customer: MVR GmbH

Period: 02.10.2009 – 29.12.2009

Android VoIP softphone app

Development of a native VoIP softphone for SwyxWare. Custom SIP stack modifications, iOS-parity history management, server synchronization for contacts/favorites, and seamless integration of Android Bluetooth and car audio stacks for headsets.

Architecture and end-to-end development of a native Android VoIP softphone client tailored for enterprise integration within the SwyxWare PBX environment. Designed and executed deep modifications to the SIP communication stack to accommodate proprietary Swyx protocol deviations, ensuring rock-solid registration, signaling, and call handling. Developed a sophisticated UI layer and engineered a complete overhaul of the history management subsystem to achieve strict iOS cross-platform parity. Implemented a robust audio routing architecture featuring tight integration with the Android Bluetooth stack (managing HFP/A2DP profiles for wireless headsets) and car audio systems, including proper audio focus handling and hardware button routing. Implemented high-performance local database modeling and server synchronization pipelines utilizing Retrofit, Jackson2, and RxJava for enterprise contacts, recent call logs, and favorites. Ensured mission-critical application stability and maintainability through advanced dependency injection (Dagger) and comprehensive automated test suites using JUnit, Mockito, and Espresso.

Software: Android, Ansi C, Butterknife, Dagger, Database modeling, Espresso, Glide, Http protocols, Jackson2, Java, Junit Tests, Mockito, ReactiveX/RxJava, Retrofit, SIP Protocol, XML

Project management: GIT, Gradle, Jenkins, Maven, Scrum

Client/end customer: technidoo UG, Swyx Solutions AG

Period: 03.09.2015 – 02.12.2016

Certificate management

Software: Java, JavaScript JS, JavaServer Pages JSP, Java Servlets, JSON, PHP, Rest, Interface specification, sFTP, Typescript, Web application

Project management: GIT

Client/end customer: Bank-Verlag GmbH

Period: 09.10.2017 – 03.11.2017

Implementation of an UpdateManagement configuration system

Design and implementation of an update management system. Consolidated SAP customer data with IT infrastructures, license mapping, role and group management for sub-companies, audit trail, 4-eye approval, and statistics using Java, JBoss, Angular 6, and MySQL.

Consolidation of customer data from SAP with information about the customer's IT infrastructure from an update package management system. Linking the update packages with the appropriate software suites licensed by the customer. Assignment of updates to the computer systems of the desired customers (groups). Comprehensive group and rights management, access filters at the various sub-companies of CompuGroup AG, detailed audit trail, 4-Eye confirmation and statistical evaluation of the installation status of the various software packages.

Software: Angular 6, CSS, Java, JavaScript JS, Java Servlets, JBoss, Jetty, MySql, ReactiveX/RxJava, SAP environment, Interface specification, SCSS, Typescript, Web application, Web service, Web-Templating

Project management: Confluence, GIT, Jira, Maven

Client/end customer: CompuGroup Medical AG

Period: 18.06.2018 – 28.09.2018

Further development of a house control app

Enterprise evolution and legacy migration (GCM to FCM) of a KNX smart home app for heterogeneous hardware. Delivered WebRTC video streaming for IP intercoms, IoT sensor integration, server-driven UI, and a resilient offline-first architecture.

Comprehensive enterprise-grade evolution, legacy migration, and architectural modularization of a mission-critical Java application designed for holistic KNX building automation and interfacing with the Gira HomeServer. Engineered and maintained a robust multi-flavour architecture enabling a unified codebase to power highly heterogeneous hardware targets—ranging from fixed in-wall wall tablets and the dedicated KNX room control device Gira G1 to mobile Android smartphones. Spearheaded the design and implementation of low-latency real-time media streaming modules for IP door intercom systems utilizing WebRTC, securely integrated across network segmentations and specialized firewall architectures (Gira F1 Bridge). Implemented low-level, hardware-adjacent IoT sensor logic for device-context awareness, including proximity detection for automated display wakeup/dimming and the end-to-end architecture of an automated, adaptive day/night mode driven by ambient light sensors. Designed a server-driven UI configuration engine where layout definitions, control states, heating/blinds telemetry, and statistics were dynamically parsed, bound, and rendered from the Gira HomeServer backend. Engineered a resilient offline-first architecture to guarantee uninterrupted operation during network outages, featuring local state persistence, background reconciliation queues, and automated UI re-configuration upon server reconnection. Executed a critical legacy migration of the push notification infrastructure from Google Cloud Messaging (GCM) to Firebase Cloud Messaging (FCM), alongside deep structural modularization to eliminate tight coupling, resolve concurrency bottlenecks, and streamline complex inter-process and inter-module communication.

Software: Android, Java, Kotlin, Rest, Web service

Project management: CI/CD, Confluence, GIT, Gradle, Jenkins, Jira, Scrum, SVN

Client/end customer: Gira Giersiepen GmbH & Co. KG

Period: 01.10.2018 – 31.08.2020

Identification and evaluation of trading strategies for the stock market

Development of a desktop application for evaluating and backtesting stock market trading strategies. Implemented deep learning components and a high-performance Java Swing custom graph painter for detailed result visualization using XML data.

Architecture and standalone development of a high-performance desktop application dedicated to the systematic discovery, backtesting, and evaluation of stock market trading strategies. Integrated deep learning models for predictive pattern recognition. Designed and engineered a custom, responsive user interface using Java Swing, featuring a dedicated, highly optimized graph painter component for smooth real-time graphical visualization of multi-variable financial charts, performance metrics, and simulation results. Managed data exchange, state persistence, and configuration structures via XML data models.

Software: Deeplearning, Desktop application, Java, Java Swing, XML

Client/end customer: Crystalline Analytics Ltd.

Period: 15.12.2020 – 31.12.2022

High-Secure smart building update management

Development of a high-security software update management system for military infrastructure and bunkers using a zero-trust architecture. Engineered multi-level, encrypted software updates by authorized technicians via USB tokens and sFTP.

Architecture and backend development of an ultra-secure software update management system tailored for military installations and underground bunker infrastructure under strict government security clearance protocols (SÜ2). Designed and enforced a strict zero-trust operational model to mitigate physical and cyber-attack surfaces. Implemented a multi-tier authorization and verification pipeline allowing software updates to be executed solely by vetted technicians using cryptographic security keys stored on physical USB hardware tokens. Developed core server-side logic (JavaServer Pages, Java Servlets) and secure sFTP data transfer and validation routines in hardened Linux environments.

Software: JavaServer Pages JSP, Java Servlets, Linux, sFTP

Project management: GIT

Client/end customer: Breuer Nachrichtentechnik GmbH

Period: 15.07.2021 – 30.09.2021

Development of entry and processing of "hardship case" for authorities

Development of a digital application and case management platform for public authorities (hardship commission for foreign nationals) using the Lucom platform. Implemented complex multi-step workflows with loop logic for staff and external board access.

Architecture and backend implementation of a highly complex e-government web application designed for digital case processing and application management within official hardship procedures for foreign nationals, utilizing the Lucom Interaction Platform. Engineered sophisticated multi-step workflow logic featuring iterative review loops, return paths, and status transitions for internal case workers. Integrated secure external access channels for members of the hardship commission to enable decentralized evaluation, commenting, and decision-making. Managed server-side document processing, web templating, and interface design (HTML/CSS/SCSS, JavaScript) across Linux and Tomcat server environments.

Software: CSS, Document-Processing, Html, Java, JavaScript JS, Linux, Linux Administration, Lucom, SCSS, Tomcat, Web application, Web-Templating

Project management: Confluence, GIT, Jira, Maven

Client/end customer: Proximity GmbH

Period: 06.09.2021 – 30.11.2021

System Architecture Datawarehousing

Redesign of the data warehousing system architecture focusing on extreme performance optimization. Comprehensive analysis of legacy workflows, achieving a 300+ fold acceleration in data processing (reducing runtime from 22:40 min to 4 sec) using Java, Spring, and advanced SQL for massive infrastructure savings.

End-to-end analysis, reengineering, and redesign of the enterprise system architecture for data warehousing, focusing on drastic performance scaling and infrastructure cost reduction. Conducted deep-dive audits of existing system bottlenecks, data processing pipelines, and query inefficiencies. Architected and implemented a high-performance processing engine utilizing Java, Spring, and advanced SQL optimization techniques. Achieved a breakthrough performance acceleration of over 300x, successfully reducing critical data batch processing times from 22 minutes and 40 seconds down to just 4 seconds. This architectural transformation delivered immediate, significant reductions in server infrastructure overhead and operational resource consumption.

Software: Java, Java Spring, SQL

Project management: CI/CD, GIT, Jira, Maven

Client/end customer: targit GmbH

Period: 01.02.2022 – 30.06.2022

Frontend for document aggregation

CMS editor for updating a jusritic expert system from new given documents (PDF)

Update of a jusritic expert system from new given documents (PDF). Detection and merging of all changes (incl. new chapters and shifts). Clear display of conflicts and marking of all detected changes.

Software: Content management CMS, Desktop application, Document-Processing, Java, Java Swing, PDF, Interface specification, Threads

Project management: GIT, Jira, Maven

Client/end customer: EQS GmbH

Period: 15.11.2022 – 28.02.2023

Development of a form system for governments

Development of complex public authority form workflows using the Lucom platform (incl. "Mein Unternehmenskonto", IfSG, foundation forms). Implementation of SAML/oAuth, Apache FOP PDF generation, Java web apps, Tomcat, and Docker on AWS.

Architecture, development, and scalable backend implementation of complex public sector online form workflows and digital application portals (e.g., for IT.NRW) using the Lucom Interaction Platform. Realized mission-critical e-government applications including the integration of "Mein Unternehmenskonto" (BundID/ELSTER identity structures), the IfSG (Protection against Infection Act) form, and specialized foundation application forms. Implemented secure authentication and authorization workflows utilizing the SAML protocol and oAuth. Engineered server-side document processing pipelines for the automated generation of official PDF notices and application documents via Apache FOP and web templating (HTML/CSS/SCSS, JavaScript). Managed containerization, Linux administration, and deployment of enterprise Java web applications across scalable Apache Tomcat and Amazon Web Services (AWS) environments, integrated with continuous delivery pipelines via Docker and Maven.

Software: Amazon Cloud AWS, Apache FOP, CSS, Docker, Document-Processing, Html, Java, JavaScript JS, Linux, Linux Administration, Lucom, oAuth, SAML Protocol, SCSS, Tomcat, Web application, Web-Templating

Project management: CI/CD, Confluence, GIT, Jira, Maven

Client/end customer: InterOne GmbH

Period: 01.06.2023 – 30.06.2024

Museum application for interactive visitor communication

Design of an interactive visitor communication app on industrial PCs. Implemented a system lockdown for 24/7 operation, a local editorial backend with auth and bad-keyword filters, real-time input sanitization, and automated dynamic beamer projection.

Architecture and comprehensive development of an interactive visitor communication and moderation platform running on secured industrial touch PCs and kiosk hardware. Engineered a robust, custom Android system lockdown to guarantee secure 24/7 public exhibition operation. Designed a hidden, local editorial backend featuring two-tier authentication (Admin/Editor roles), a configurable bad-keyword filter, and dynamic styling options. Implemented advanced, real-time input sanitization directly within the edit fields (blocking emojis, repetitive special characters like *, and excessive whitespace while preserving manual line breaks and text length limits) alongside multi-language support (including Arabic layout handling via Google Keyboard). Developed an automated dynamic scaling and projection algorithm that outputted approved visitor comments via beamers as visual text blocks, inversely scaling font sizes relative to text length for optimal legibility. ​Software: Android, JetPack, JetPack Compose, Kiosk Lockdown, Kotlin, Multi-threading, XML, Custom Input Filtering, Dynamic UI Scaling

Software: Android, JetPack, JetPack Compose, Kiosk system, Kotlin, Threads, XML

Client/end customer: Museumsverein Morsbroich e.V.

Period: 07.05.2025 – 14.08.2025

DHL Android App

Enhancement of the enterprise delivery driver app on Zebra handhelds with a primary focus on tracking down and fixing rare, critical bugs. Handling offline-online state synchronization, route management, locker workflows, and Bluetooth label printing via ZPL/CPCL.

Further development, stabilization, and architecture optimization of the mission-critical DHL delivery driver application running on Zebra handheld devices. Focused on mastering complex, real-time data flows within a sophisticated multi-threading environment. Responsibilities included robust handling of live barcode scans, seamless offline-online state synchronization, dynamic route management, and logistics workflows for servicing and filling DHL service point lockers. Additionally, implemented a stable print history and reprint mechanism communicating directly via Bluetooth with mobile label printers utilizing text-based ZPL/CPCL print commands.

Software: Android, Android Koin, JetPack, JetPack Compose, JSON, Junit Tests, Kotlin, Interface specification, Threads

Hardware: Bar code

Project management: Confluence, GIT, Gradle, Jira

Client/end customer: DHL Paket GmbH

Period: 01.02.2026 – 15.06.2026