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Christian SiefkesCS

Christian Siefkes

Senior Backend Developer & Data Engineer

680 €/Tag
Berlin, DE
8-15 Jahre

Durchschnittliche Reaktionszeit: 1h

Über Christian

• PhD in Computer Science, specialized in machine learning (ML) and artificial intelligence.
• 20+ years of professional experience as backend developer and software engineer, freelancing since 2006.
• Strong expertise in Python-based data processing and ML pipelines, including NumPy, Pandas, PyTorch, and scikit-learn.
• Extensive backend experience with SQL (especially PostgreSQL), RESTful APIs (including with FastAPI and Flask), and cloud-native systems (AWS, Supabase).
• Designed and deployed production-grade ML microservices for document classification, data extraction, and sentiment analysis.
• Familiar with containerized deployment and orchestration (Docker, Kubernetes, Helm).
• Worked in remote, agile teams on high-impact projects for major clients.
• Proficient in additional languages including Java, JavaScript, Haskell, and Ruby.
• Experienced in performance profiling and optimization, both in database and code-heavy contexts.
• Languages: German (native), English (near-native level).
• Available in Berlin and remote.
  • Deutsch

    Muttersprachlich oder zweisprachig

  • Englisch

    Verhandlungssicher

Vor Ort möglich
Berlin (bis zu 50 km)

Projekt- und Berufserfahrung

  • Ragspero, a RAG (retrieval-augmented generation)AI chatbot framework
    Independent open source project, scheduled for release in spring 2026
    SOFTWARE-HERSTELLER
    März 2025 - Heute (1 Jahr und 3 Monate)
    Berlin, Deutschland
    • Processes PDF, HTML, and other file formats to build a custom knowledge base for domain-specific chatbots.
    • Supports multiple languages, with English and German built-in.
    • Built in Python based on Kotaemon, LangChain, FastAPI, Qdrant, and SentenceTransformer.
    • Integrates Gemini, Ollama, or other pluggable LLMs.
    • Runs locally or as a public web service.
    Python FastAPI LLM Langchain
  • ACB Studio
    PostgreSQL backend developer
    SOFTWARE-HERSTELLER
    Februar 2024 - November 2024 (10 Monate)
    Düsseldorf, Deutschland
    • Rewrite of the mytischtennis.de website with an high-performance database-first backend written in PostgreSQL and PL/pgSQL.
    • Creation of payment and order workflows integrating PayPal and PayOne as payment providers.
    • Retrieval of data from external systems using Postgres caching for fast access times.
    Docker PostgreSQL Supabase SQL Payments
  • T-Systems International
    Python/Pandas developer and data scientist
    SOFTWARE-HERSTELLER
    April 2023 - Dezember 2023 (7 Monate)
    Frankfurt am Main, Deutschland
    • Development of SPACE (Statistical Production and Compilation Environment), the new data analytics platform used by the European Central Bank (ECB).
    • Integration of various data sources from banks and statistical authorities into the ECB’s new Pandas-based data analytics platform.
    • Analysis and elimination of performance bottlenecks in the software.
    • Porting of the whole SPACE software from Pandas 1.3 to 2.1.
    Pandas Pytorch Python Performance Optimization Kubernetes

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Ausbildung und Abschlüsse

  • PhD in Computer Science
    Free University of Berlin
    2007
    Thesis title: An Incrementally Trainable Statistical Approach to Information Extraction. Thesis topic: Statistical extraction information extraction (IE) from weekly structured texts (HTML/XML) using incremental machine learning algorithms. Funded by a 3-year fellowship of the Berlin-Brandenburg Graduate School in Distributed Information Systems.
  • Diplom Studies Computer Science
    Technical University of Berlin
    2002
    Graduated as Diplom-Informatiker (Master of Science in Computer Science). Thesis title: A Toolkit for Caching and Prefetching in the Context of Web Application Platforms. Thesis topic: Using machine learning (Markov models) to predict upcoming web requests to allow faster response times.

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