Stelios is available for hire

Stelios Sfakianakis

Verified Expert in Engineering

Back-end Developer

Heraklion, Greece

Toptal member since October 31, 2022

Expertise

Back-end Developers REST API SQL Machine Learning Web Scraping Git Python C PostgreSQL C++Redis Java Qt Development Node.js OAuth

Bio

Stelios is a professional software engineer with 12+ years of experience, a master of science degree in computer science, and a PhD in bioinformatics. He is an expert in designing and implementing REST APIs and microservices using Python, Java, and Node.js and several databases like PostgreSQL, MySQL, Cassandra, and CockroachDB. Stelios also has extensive data analytic experience in R, SQL, and scikit-learn for machine learning tasks.

Portfolio

National Research Center

Web Architecture, System Design, Architecture, Python, APIs, Back-end...

Self-employed

WordPress, Front-end Design, HTML, Tailwind CSS, REST

Freelance Clients

C++, Qt, Java, JavaScript, Desktop App Development, Web Scraping

Experience

REST - 10 years
REST APIs - 10 years
Python - 10 years
PostgreSQL - 8 years
Web Architecture - 8 years
System Design - 8 years
SQL - 8 years
APIs - 7 years

Availability

Part-time

Preferred Environment

Git, MacOS, Visual Studio Code (VS Code)

The most amazing...

...open source software I've released is a PostgreSQL extension developed in C as a foreign data wrapper to access a remote RESTful API using SQL.

Work Experience

Principal Engineer

2010 - PRESENT

National Research Center

Worked on many integration projects that required efficient management of multimodal clinical data.
Designed system architectures using the principles of domain-driven design and microservices.
Implemented many services that support standardized APIs in the health IT domain from scratch, including IHE profiles and HL7 specifications.

Technologies: Web Architecture, System Design, Architecture, Python, APIs, Back-end, Leadership, REST APIs

Web Developer

2019 - 2021

Self-employed

Designed multiple websites using WordPress, enabling users to edit and publish content.
Implemented a custom WordPress plugin to show the client's personnel according to the designed theme.
Used static website generators, like Eleventy, to develop custom websites, mostly with static content.

Technologies: WordPress, Front-end Design, HTML, Tailwind CSS, REST

Software Developer

2018 - 2021

Freelance Clients

Developed a complex desktop-native graphical user interface with C++11, Qt as the GUI framework, and PostgreSQL as the database.
Implemented a macOS installer to install the latest version of PostgreSQL and update the app and the database.
Provided user support using Jira to track and fix bugs and issues.

Technologies: C++, Qt, Java, JavaScript, Desktop App Development, Web Scraping

Experience

Desktop applications with C++ and Qt

https://culturalheritageimaging.org/What_We_Offer/Downloads/DLN/index.html

Developed a complex cross-platform desktop application graphical user interface with C++11, Qt as the GUI framework, and PostgreSQL as the database. For this application, I also developed a macOS installation package for the users to download and install everything, from the PostgreSQL RDBMS to the database schema creation and the application itself.

Implementation of an OpenID Connect Server

As part of a research project, I implemented an OpenID Connect server from scratch that links users to the federated login of large European Research Infrastructures. The implementation was based on Node.js using JSON Web Tokens signed by the server's private key to make them stateless. The underlying data store was a PostgreSQL database.

Foreign Data Wrapper for OpenCageData API

https://github.com/sgsfak/ocgeo_fdw

The OpenCage Geocoding API provides reverse and forward geocoding via a RESTful API (opencagedata.com/api).

I built a PostgreSQL extension that wraps the OpenCageData API as a foreign data wrapper (FDW), which allows the transparent use of the API from inside a PostgreSQL database and its integration with existing tables. This extension is released as open source software under the terms of the PostgreSQL License.

Implement a Stacking ML Classifier in Scikit-learn

https://github.com/sgsfak/subnet_stacking

"Stacked generalization" was introduced by Wolpert in 1992 as a way to combine multiple "base" classifiers in a two-level classification scheme. In this project, I implemented it from scratch and integrated it with the scikit-learn machine learning framework in Python.

Education

2010 - 2015

PhD in Bioinformatics

Technical University of Crete - Chania, Greece

1995 - 1999

Master's Degree in Computer Science

National and Kapodistrian University of Athens - Athens, Greece

Skills

Libraries/APIs

REST APIs, Node.js, Scikit-learn

Tools

Git

Languages

SQL, Python, C++, C, Java, JavaScript, R, HTML

Paradigms

Web Architecture, REST, Desktop App Development

Frameworks

Qt, OAuth 2, Tailwind CSS

Platforms

Visual Studio Code (VS Code), MacOS, WordPress

Storage

PostgreSQL, Redis

Industry Expertise

Bioinformatics

Other

Back-end, Information Systems, Machine Learning, Statistics, Architecture, APIs, OpenID Connect (OIDC), Leadership, Web Scraping, Front-end Design, System Design, Genomics

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