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Senior Full-Stack Engineer -

Martin Grellmann.

S/4HANA Development, SAP BTP, enterprise APIs and clean-core aligned full-stack engineering.
20+ years in software engineering with recent specialization in modern SAP full-stack development.
ABAP, CDS, OData, RAP, CAP, Fiori / UI5, SAP BTP and S/4HANA modernization.
Strong additional background in JavaScript, TypeScript, React, Node.js, PHP, Drupal and REST integration.
Focused on scalable business applications, maintainability, clean code and sustainable architecture.

About me

German citizen with unrestricted work and residence permit in Brazil. Senior software engineer with 20+ years of experience in full-stack web development and recent specialization in modern SAP full-stack development, including SAP BTP, S/4HANA modernization, ABAP, CDS, OData, Fiori/UI5 and API integration.

Location:Goiás, Brazil and Leipzig, Germany
Nationality:German citizen / unrestricted work and residence permit in Brazil
Specialization:Senior Full-Stack Engineer, SAP BTP, S/4HANA, enterprise APIs, clean core
Experience:20+ years software engineering and full-stack development
Architecture:iSAQB CPSA-F Foundation Level training completed, exam planned for Q3 2026
Certifications:Scrum Master PSMI, Full-Stack Web Developer certification
Methods:Clean Code, SOLID, refactoring, code reviews, sustainable architecture
Education:Industrial Clerk (2002 - 2004)

Summary

Senior Full-Stack Developer with 20+ years of experience in software engineering and focused modern specialization in SAP full-stack development across SAP BTP, S/4HANA, ABAP, CDS, OData and Fiori/UI5.

Early adopter of modern SAP technologies including RAP, CAP, ABAP Cloud and SAP BTP. Strong conceptual understanding, hands-on experimentation and extensive experience in enterprise software architecture, API integration and clean, maintainable application development.

Senior SAP Developer

Intecsoft GmbH & Co, Dresden, Germany•01/2025 - Present

Contract-based SAP development role focused on modernization and integration in S/4HANA-related projects.

Improved backend API interfaces in an S/4HANA project to increase integration readiness and maintainability, supported productive web services during hypercare in the FI environment and refactored a SAP Business Suite Dynpro application into object-oriented ABAP for better maintainability and future S/4HANA compatibility in an IS-U context.

Technical Lead / IT Specialist

Ferienhausvermittlung fincaferien, Düsseldorf, Germany•03/2025 - Present

Lead technical modernization and digital transformation of a multi-site vacation rental platform based on Drupal.

Designed and implemented a cloud-based infrastructure strategy, created a modernization roadmap for the legacy platform architecture, developed API-driven integrations and supported digitalization initiatives across booking, content and operational workflows.

SAP Technical Consultant, SAP Full-Stack Development

BA Business Advice GmbH, Oldenburg, Germany•02/2022 - 12/2024

SAP consulting and development with focus on ABAP, UI5, Fiori, S/4HANA, SAP BTP and modern extension models.

Developed and enhanced SAP applications using ABAP, CDS, OData and UI5, contributed to ERP-to-S/4HANA migration projects, refactored existing applications and worked on side-by-side and developer extensibility scenarios in S/4HANA Public Cloud.

Software Developer and Linux Administrator

Sengicon GmbH, Leipzig, Germany•02/2021 - 01/2022

Full-stack development in an Industry 4.0 environment with React frontends, PHP backends, API integration and Linux-based infrastructure.

Successfully converted an outdated PHP web application to a modern PHP REST backend and connected it to a newly created React web frontend including database modelling.

Webmaster / Web Developer

Ferienhaus-Vermittlung fincaferien.de GmbH, Bockenem, Germany•04/2004 - 12/2019

Long-term responsibility for web development, operations, optimization and technical infrastructure.

Developed and maintained websites and web applications with PHP, Drupal, HTML and CSS, managed Linux and network environments and improved traffic, performance and usability through technical SEO and usability-focused optimization.

Skills

The rating reflects practical experience, depth of application and long-term use in professional projects. I also indicate the approximate years of experience and the roles in which each skill was applied most strongly.

SAP development / Architecture

Web / API engineering

PHP / Drupal / Platforms

Methods / Quality

Work

Senior SAP Developer

Intecsoft GmbH & Co, Dresden, Germany•01/2025 - Present

Modernization and integration in S/4HANA-related projects.

Improved backend API interfaces in an S/4HANA project to increase integration readiness and maintainability.

Supported productive web services and API interfaces during hypercare in the FI environment.

Refactored a SAP Business Suite Dynpro application into object-oriented ABAP for better maintainability and future S/4HANA compatibility in an IS-U context.

Worked closely with business stakeholders, solution managers and developers to align implementation with functional requirements.

Skills

ABAP Objects
ABAP SQL
CDS Views
OData
SAP BTP
REST
Fiori/UI5
S/4HANA
Clean Core

Technical Lead / IT Specialist

Ferienhausvermittlung fincaferien, Düsseldorf, Germany•03/2025 - Present

Modernization and digital transformation of a multi-site vacation rental platform.

Designed and implemented a cloud-based infrastructure strategy to improve scalability and maintainability.

Designed a modernization roadmap for a legacy Drupal platform architecture, including API-driven integrations and service-oriented design.

Developed and integrated enterprise APIs connecting business services with Drupal CMS.

Drove digitalization initiatives across booking, content and operational workflows.

Skills

Drupal
PHP
Cloud infrastructure
REST APIs
Automation
Web technologies

SAP Technical Consultant, SAP Full-Stack Development

BA Business Advice GmbH, Oldenburg, Germany•02/2022 - 12/2024

SAP consulting and development with focus on ABAP, UI5, Fiori, S/4HANA and SAP BTP.

Developed and enhanced SAP applications using ABAP, CDS, OData and UI5.

Contributed to ERP-to-S/4HANA migration projects and MII-related work.

Refactored existing applications to improve maintainability, future readiness and architectural quality.

Built UI5 Freestyle and Fiori Elements applications and contributed to initiatives involving SAP BTP, RAP and CAP.

Skills

SAP ABAP
ABAP CDS
OData v2/v4
SAP UI5
Fiori Elements
RAP
CAP
SAP BTP
S/4HANA Public Cloud
JavaScript
TypeScript
Jest

Software Developer and Linux Administrator

Sengicon GmbH, Leipzig, Germany•02/2021 - 01/2022

Full-stack development in an Industry 4.0 environment.

Developed React-based web frontends and refactored and modernized existing PHP applications.

Built and integrated REST-based APIs with PHP and modelled databases with MySQL, MariaDB and PostgreSQL.

Performed testing with PHPUnit and Jest and installed, configured and administered Linux and LAMP environments.

Skills

React
JavaScript
PHP
REST
PHPUnit
Jest
Linux
Apache
MySQL
MariaDB
PostgreSQL
Composer

Webmaster / Web Developer

Ferienhaus-Vermittlung fincaferien.de GmbH, Bockenem, Germany•04/2004 - 12/2019

Web development, operations, optimization and technical infrastructure.

Developed and maintained websites and web applications with PHP, Drupal, HTML and CSS.

Customized and extended Drupal modules, managed Linux, Samba and network environments and used Git and Jira in development workflows.

Successfully increased organic traffic through targeted technical SEO strategies and enhanced website performance and user experience through usability improvements.

Skills

PHP
Drupal 7
HTML
CSS
Git
Jira
Linux
Samba
SEO/SEA

Education

Software Architect

Software Academy by intecsoft, Dresden, Germany•06/2025 - 06/2026

iSAQB CPSA-F Foundation Level training completed.

iSAQB CPSA-F Foundation Level training completed, exam planned for Q3 2026.

Agile Project Management

Indisoft GmbH, Leipzig, Germany•05/2020 - 06/2020

Scrum Master PSMI certification by Scrum.org.

Agile project management training with Scrum Master PSMI certification.

Training Full-Stack Web Developer

Indisoft GmbH, Leipzig, Germany•2020 - 2021

Full-Stack Web Developer certification.

Training covered modern web development, JavaScript, PHP, MySQL, Linux administration, content management and related best practices.

Industrial Clerk

DAA GmbH, Hildesheim, Germany•2002 - 2004

Industrial Clerk training.

Vocational education focused on business processes, commercial management and organizational foundations.

Additional

Focused on durable engineering quality, maintainability, architecture, refactoring and scalable business applications.
Available across Germany and Brazil; listed locations are Goiás, Brazil and Leipzig, Germany.
German citizen with unrestricted work and residence permit in Brazil. Languages: German (native), English (professional working proficiency).

Freelance

In principle, I am open to freelance offers. Feel free to contact me via email.

I've extensive experience and skills in responsive web design, full-stack development, JavaScript backend development, database modelling, PHP development, SAP UI5 Freestyle development, ABAP development, S/4 HANA Cloud - Public Edition Extensions, and BTP - Node development, making me a strong candidate for various freelance opportunities.