Web application net sql server databaseроботи

I am in need of an experienced developer to create a project management web application that's colorful and vibrant. My vision is to have: - Task allocation and tracking: An integrated functionality that gives us the ability to multi-task and keep track of on-going projects. - Time tracking: Time management is crucial for us, we need a system that keeps things timely and organized. Ideal candidates should have experience in developing project management software or any relevant web applications. Familiarity with a vibrant and colourful user interface is also a key requirement. Show me your relevant portfolio so we can collaborate effectively to bring this vision to life.

...HTTPS domain for our web application hosted on Google Cloud Platform (GCP). The ideal candidate should have extensive experience with GCP, CI/CD pipelines, and HTTPS configuration. Scope of Work: 1. CI/CD Implementation: - Set up a CI/CD pipeline using GitHub Actions for automated testing, building, and deployment of both frontend and backend applications. - Integrate the pipeline with our GCP infrastructure, including Compute Engine, Cloud SQL, and Cloud Storage. 2. Logging Setup: - Configure logging for all services: -- Frontend (Nginx, ): Log HTTP requests, errors, and application logs. -- Backend (Gunicorn, Django): Log application errors, access logs, and system logs. -- Celery and Beat: Log task execution and periodic tasks. -- Database...

Project Description: Mobile Application for Inventory Management Objective: Develop a Minimum Viable Product (MVP) of an Android application for inventory management and tracking using GPS and Bluetooth beacons. Technology: Flutter Key Requirements The Application -------------------------- - The app should primarily be developed in Flutter. However, since a Foreground service is required to run indefinitely in the background, it is acceptable to create this service in Kotlin or Java. Communication between Flutter and the native code should be done via Platform Channels (MethodChannel and EventChannel). User Interface ----------------------- The app should have three main screens: - Splash Screen: Displays the app logo. - Login Screen: User authentication with u...

hello I am currently planning to start a startup. I am currently entering the IT field (fields such as Facebook and Instagram) and need a programmer to join me. The working hours per day will be more...hours per day will be more than 40 hours, and a small salary may be paid per month. I have very creative ideas and am ready to grow into a global company. If you join me, I will provide you with an additional salary increase and a higher position as the company grows (e.g. Data Manager/Marketing Manager, etc.) Anyone who can do any of the following is welcome. -programmer -translator -lawyer -Server maintenance -Marketing expert -Anyone else who can contribute to the growth of the company Anyone who has a lot of passion and is starting a journey with me for my company is alway...

...specifically to people-centric management. Role and Responsibilities: As a QA (Software Tester) at PiipAi, your role is pivotal in ensuring the quality and reliability of our software. You will work closely with our development team to meticulously test and validate our applications, identifying and rectifying any issues that may arise. Key responsibilities include: - Conducting rigorous testing across our web applications to detect and report bugs. - Collaborating with developers to ensure seamless integration and functionality. - Employing your strong analytical and strategic thinking to formulate effective testing strategies. Requirements: We are seeking an individual who possesses: - Very good knowledge in various testing methodologies, frameworks, and tools. - Good knowledge...

I am on a quest for an exceptional individual who can collaborate with me in writing a presentation about chaos engineering and incident management specifically for a .Net driven distributed monolith. Key points include: - The purpose of the presentation is to educate stakeholders and instigate a beneficial scenario discussion, leading us on a path to implementation. - The target audience has an intermediate understanding of chaos engineering and incident management, hence the presentation should be calibrated to this level. - The presentation will heavily emphasize on the practical aspects of chaos engineering and incident management. Focal themes would be implementing chaos engineering, simulating incidents, and strategies for mitigation. To ensure a successful project, you ide...

use Oracle PL SQL teach me how to install free Oracle DB on my local windows 11 acceptance: I can run your code on my computer ; all code work on my computer when I run it by myself You have 2 days you provide code to simulate input data (both code versions: python and sql)-> transactions data *****you provide SQL code to calculate per day summary for each day for each product for each store for 3 years SIMULATION data for 3 years 100 products 20 stores 5 USA states random dates and prices promotion for 30 promotions per year , each promotion happen for 7 to 15 products, for example promotion at may 10, 2023 happen for product ids: 34, 65, 12, 78, 5, 23, 41. When 34 for 20%; 65 for 30%; 12 for 40%; 78 for 10%; 5 for 15%; 23 for 70%; 41 for 30% randoml...

hello We are currently looking for someone to manage the server that will run our website and app. (Please enter “ITO” to confirm) -Work: Anywhere you want -Job description: Manage everything from server hosting to operation In particular, maintenance/repair to ensure that security is very strong. Video conference once a week Submit work details and inspection results as a report every three days -Salary: $100/month ((Budgets may continue to increase as the company grows in size and sales increase))

I require an advanced database to streamline church operations. It must include: - Member management: This involves recording personal details of each member, tracking attendance, and allocating to the right departments. Each member's record should also include household and family details, with specific fields for spouse and children. - Functionalities: Capacity to sort data based on each individual (organize by member). It should also capture other input fields like gender, age, membership status, notes, and whether they serve as workers or ministers. - Financial management: The platform should have capabilities for recording and tracking financial contributions. Ideal freelancers will have experience in building similar database systems, with a keen understanding ...

I'm interested in application development for both Android and iOS platforms. The key feature is to allow sending SMS messages to a selected database. Any professional stepping into this project should be able to handle: - Database development: The backend needs to be designed to store contact details efficiently. Expectation is to accommodate less than 100 contacts initially, with potential for future expansion. Strong database management skills are a prerequisite. - App development: Looking for someone with profound knowledge of Android and iOS app development. Familiarity with SMS integration in apps is essential. Don't shy away from illustrating your previous experience in similar projects when bidding.

We are looking for 5-10 years of .Net experienced developer who can also have experienced in React and .Net based web development. Long terms multiple projects development. Using Mainly Azure SQL server database with Visual Studio .Net Core API. Graph QL and EF. Worked on Azure Key Vault, Azure Logic app, Azure function is bonus.

use Oracle PL SQL teach me how to install free Oracle DB on my local windows 11 acceptance: I can run your code on my computer ; all code work on my computer when I run it by myself You have 2 days *****you provide code to simulate input data -> transactions data *****you provide SQL code to calculate per day summary for each day for each product for each store for 3 years SIMULATION data for 3 years 100 products 20 stores 5 USA states randomly 30 to 170 transactions per day for given product for usual price randomly 200 to 600 transactions per day for given product for promotion random dates and prices promotion for 30 promotions per year , each promotion happen for 7 to 15 products, for example promotion at may 10, 2023 happen for product ids: 34, 65, 12, 78,...

I am looking for a developer with experience on modding Call of Duty Black Ops 2 and bot development on Discord. The project objectives include: CUSTOM IN-GAME COMMANDS AND PERKZ - Creating custom Plutonium server settings for Black Ops 2 Zombies. - For the commands, i want there to be the basic commands that anyone can use, and “vip” commands for the players who have vip role. - Most if not all of the custom perks scripts i want have already been published on the plutonium forum. - Also needs stats tracking DISCORD BOT - Developing a Discord bot capable of linking a player's Discord account to their in-game GUID. - Granting players access to vip in-game commands thru the discord bot - in-game points rewards for when a player links their discord account to the...

I'm in need of a skilled full-stack developer to create a website that is primarily aimed at monitoring ...uymbai The target audience for this website is less than 10 employees so the system should be designed to handle this scale effectively. Additionally, the website should be able to generate daily reports based on the tracked data. This will help me keep tabs on the efficiency and productivity of my team on a daily basis. Ideal skills and experience for the job would include: - Proficiency in web development technologies - Previous experience in developing similar systems - Strong understanding of user experience principles - Ability to integrate reporting features into the system If you're confident in your abilities to deliver such a product, I'm looking for...

...ready, and the SQL tables have been set up. The main features of this project include: - **Dashboard:** This should display data from the other 3 pages in a list format as well as in a bar chart. - **Page 1 - Callback List:** A simple list of data from the 'callback' table. - **Page 2 - Token List:** A simple list of data from the 'token' table. - **Page 3 - Name List:** A simple list of data from the 'name' table. For the dashboard, I'm looking for a clean, professional design and prefer the use of bar charts for the graphical representation of the data. User authentication should be straightforward, requiring only an email and password for access. Ideal Skills and Experience: - Proficient in Laravel - Experience in creating admin dash...

...what you'll be doing -Number of positions: 5 (subject to change) -Tasks: Preventing hacking / preventing data leakage / monitoring servers in real time / modifying and maintaining websites / adding new website features / developing new web and app features / increasing server security / ensuring compliance with privacy laws .... and most other services required to run apps and websites. -Meetings: All work is done at your location, and once every 7 days, we have a video conference with all developers, and you can send us a report of your daily work and server checks. (Time and more information to follow) -Budget: $150~$200/month/1 person (subject to adjustment) -We still have a lot of time before monetization, so please take your time bidding. Also, everything ...

We have a project developed with VS2022, c#, datatables, SQL database, javascript and similar.... The user experience is not good. We need a professional and nice interface and user experience, but, mantain our actual code and funcionality.

Hi, I am looking for a developer to maintain, make upgrades and fix bugs on my current website and booking system. The system has been done in SQL written in C# by my old developer. He has had a change of career and can no longer work on things but is happy to do a handover to make things easier. This will be an ongoing business relationship and not a one off thing so will need someone with good communication and accurate times of completion. Thanks, Luke.

I am looking for an experienced CodeIgniter developer to upgrade my existing CodeIgniter 3 project to CodeIgniter 4. The project is currently live and needs to maintain the same database structure and functionality. The key tasks include: Upgrade CodeIgniter Version: Migrate the entire project from CodeIgniter 3 to CodeIgniter 4, ensuring all features and functionalities remain intact. Optimize SQL Queries: Review and optimize all SQL queries to handle heavy loads efficiently. The current system experiences performance issues during peak times, and the new version should resolve these. Fix Bugs and Security Issues: Identify and fix any existing bugs and security vulnerabilities in the current project. Ensure the new version adheres to the latest security standards. ...

...with expertise in both User Interface (UI) and User Experience (UX) for a web application. The primary goal of the project is to elevate user engagement and enhance usability. Ideal Skills and Experience: - Proven UI and UX design experience specifically for web applications - Ability to understand and incorporate strategies for increasing user engagement - Competence in improving the usability of digital tools - Proficiency in wireframing and prototyping, and iterative design - Comprehensive portfolio showcasing relevant work Your responsibility will be to design an intuitive, engaging interface that maximizes user engagement and improves the usability of the application. A clear understanding of web application usability standards is requir...

It is necessary solve two bugs to a Laravel application regard the frontend of condition use php 7.4. if it is necessary you must do changes to the database and the backend

I need an experienced Linux admin who can help me set up a CentOS server to function as a web, database, and file server. The ideal candidate will be familiar with CentOS and have experience configuring a server with multiple services. Key Requirements: - Install and configure CentOS on a server - Set up Nginx as the web server - Configure the server to also function as a database and file server - Ensure the server is secure and optimized for performance - Provide documentation of the setup and configuration for future reference.

I am looking for a skilled Elasticsearch expert to help with data indexing and analysis for a large dataset. The data to be indexed is primarily textual and it is sourced from database entries. Experience with database management and textual data analysis is a crucial requirement for this project. The primary tasks include: - Analyzing and indexing a large dataset from database entries - Setting up Elasticsearch for efficient data analysis - Implementing indexing strategies for textual data Proficiency in Elasticsearch, data indexing, and database management is benefit for this project. Familiarity with handling large datasets and textual data is a must.

I'm seeking a data entry specialist with a knack for precision to type data from PDFs into an online database. Key Requirements: - As a data entry specialist, you will be responsible for the accurate and timely entry of data from PDFs into our online database. - The data format should match the original PDFs, with no specific validation rules needed. - The ideal candidate will be detail-oriented, with a proven track record of data entry. If you're someone who enjoys working with data and has an eye for detail, this could be an ideal project for you.

...investments and to help me make informed decisions. Key Areas: - Evaluating Investment Opportunities: I need someone who can create robust and reliable financial models to assess the viability of various real estate ventures. Your models should help me identify and prioritize the most promising investments. - Financial Metrics: Your models should primarily focus on Return on Investment (ROI), Net Present Value (NPV), and Capitalization Rate (Cap Rate). These are the key metrics I need to see to make sound investment decisions. Ideal Candidate: - Proven Experience: Previous experience in real estate financial modelling and investment analysis is a must. A background in real estate or finance would be highly beneficial. - Analytical Skills: A sharp mind for identifying trends,...

Hi there! I'm seeking an expert in Python and VBA who can develop a real-time data statistical analysis tool for use on Windows. The tool must be able to process financial data. Though the format of my data wasn't specified, please be ready to handle a diverse range of formats, including but not limited to CSV files, SQL databases, and Excel files. Skills and Experience: - Mastery of Python and VBA - Experience with statistical data analysis - Familiarity with financial data - Proficiency in handling diverse data formats. - Skill in working on Windows OS. Ultimately, I require a reliable system for my ongoing financial data analysis needs. Your track record of similar successful tasks will be a plus.

I'm seeking an expert in Python and VBA who can develop a real-time data statistical analysis tool for use on Windows. The tool must be able to process financial data. Though the format of my data wasn't specified, please be ready to handle a diverse range of formats, including but not limited to CSV files, SQL databases, and Excel files. Skills and Experience: - Mastery of Python and VBA - Experience with statistical data analysis - Familiarity with financial data - Proficiency in handling diverse data formats. - Skill in working on Windows OS. Ultimately, I require a reliable system for my ongoing financial data analysis needs. Your track record of similar successful tasks will be a plus.

...NET 3.5 application from a 2008 server to a dedicated server. Key Requirements: - Migrate ASP.NET 3.5 application: The current application is running on ASP.NET 3.5 and needs to be seamlessly moved to the new dedicated server. - Hosting Environment: The application should be set up on a dedicated server. Experience with dedicated servers is crucial. - Identify Specific Requirements: I'm unsure of any dependencies or specific requirements the application might have, so the ideal candidate will need to assess this and make necessary recommendations. Ideal Skills & Experience: - Proficiency in ASP.NET 3.5: Extensive experience with ASP.NET 3.5 and above is essential. - Server Migration: Proven track record of...

I'm in need of an exceptional landing page that focuses on promoting my product. While I have some branding elements like color schemes and logos, I'm open to creative interpretations within this framework. Key Requirements: - The main objective is to showcase the features of the product in an engaging and visually appealing way. - The landing page should also have a contact form integrated for lead generation and customer inquiries. Ideal Candidate: - Previous experience in creating engaging and conversion-optimized landing pages is crucial. - Strong understanding of user experience and design principles. - Ability to work within existing branding guidelines while adding a creative touch. Please provide examples of your previous landing page designs and any relevant experie...

I'm looking for a seasoned developer to create a desktop application focused on data management. This software will be used on the Windows operating system and must be developed using Java. The ideal candidate will have: - Extensive experience with Java and Windows development - A deep understanding of data management systems - The ability to work effectively and communicate progress regularly Please provide a clear demonstration of your skills in these areas when submitting a proposal, we are looking for the best development talents to execute this project.

I'm looking for a developer to create a VPN application that will run on both IOS and Android. This application should support both SoftEther VPN Protocol and OpenVPN. Key features to be included: -Protocols: Support both SoftEther VPN Protocol and OpenVPN. - Data encryption: An essential feature for securing users' data - Kill switch: A crucial function that ensures users' internet traffic is cut off should the VPN connection fail - Multi-location support: The VPN should offer various server locations for users to connect to securely The ideal candidate should have experience in developing applications for both IOS and Android, as well as prior experience in VPN development. A strong understanding of network security concepts and protocols is a must. ...

I'm in need of a developer to set up user roles in my new spring application like they were in the old struts application. Key Project Details: - Setting up roles: I require the creation of Admin, User, Manager, and Supervisor roles with the same permissions as in the old struts application. - No additional roles: The only additional role needed is 'Supervisor'. I do not require Developer or Guest roles. Ideal Freelancer: - Proficient in Java, particularly Spring Framework. - Proven experience in role-based access control. - Familiarity with legacy system migration. - Good understanding of the Struts framework (for comparison purposes). - Strong communication skills for clarification and updates.

I'm in need of a Flutter Developer to assist with updating our existing Art Prizes app for both iOS and Android. We've made additions to the underlying .NET solution and now require integration of new pages and features. It's crucial that you have a solid understanding of Flutter as well as knowledge on integrating APIs. Previous experience in updating existing apps and implementing push notifications is highly desired. If you don't have a rating of 4.9 or higher I won't be contacting you. You will have a formal process for versioning the iterations and you will have inhouse testing available. If you deliver an initial solution that is full of bugs we won't continue working with you. First deliverable will be the IOS version FOLLOWED by the android ...

I'm in need of a creative professional who can both design large, eye-catching logos and apply them to T-shirts. Desired skills and experience for this project include: • Graphic design: As the logos are yet to be designed, your expertise in creating memorable and visually striking images will be critical. • Knowledge of textiles: Understanding how your designs will translate when printed onto fabric will make a significant difference to the finished product. • Experience in screen printing: To ensure the large logos are applied accurately and effectively on the T-shirts. • Attention to detail: Your meticulous eye will ensure the final product looks exactly as envisioned. Applicants with examples of previously designed logos and printed apparel will be preferred....

I'm in need of a Machine Learning professional who is well-versed in applying SHAP (SHapley Additive exPlanations). Primary Responsibilities: - As the heart of this project involves building Machine Learning models, your role would be crucial in shaping the final product. - I am particularly interested in leveraging the Random Forest Algorithm that would be applied to structured data, encompassing numbers and categories. Essential Skills: - Proficiency in the ML Algorithm - Sound understanding of structured data - Proven experience with SHAP Your expertise will indeed be paramount to this project. As we plunge deeper into the data, your insights and guidance will undeniably lead us towards success.

Build an ISO for a raspberry pi (with cellular notecard) to scan for unique cell phones in a specific range and log the unique phone ID and timestamps/ping (distance) from the raspberry pi and store in mysql database using cellular adapter.

I'm seeking a specialist to locate a VPS/VRoot server that can provide minimized latency to a website origin hidden behind a Cloudflare proxy. The task encompasses: - Identifying the server with the lowest possible ping based in Europe. - The server should run on a Windows operating system. - The ultimate objective is to improve user experience by minimizing latency. Ideal freelancers for this job will have a robust understanding of server locations, operating systems and how they interplay with website latency. Experience with Cloudflare proxies, Windows-based servers, and in-depth knowledge on achieving optimal latency is distinctly beneficial. The website would be and I require the lowest ping when buying an item on the sites trading page. Ping can b...

...biodiversity net gain consultancy report. The aim is to formulate effective strategies for enhancing biodiversity within protected natural habitats. Ideal freelancers for this project are: - Qualified environmental scientists or ecologists. Preferably, with a strong understanding of conservation management strategies. - Those with prior experience in drafting biodiversity net gain reports, particularly related to natural habitat preservation. - An understanding of various habitat types would be beneficial, although not essential as the habitat type hasn't been specified in this instance. Key responsibilities: - Evaluate the current state of biodiversity within the specified natural habitat areas. - Propose well-researched, achievable strategies for improving biod...

I need an experienced Linux admin who can help me set up a CentOS server to function as a web, database, and file server. The ideal candidate will be familiar with CentOS and have experience configuring a server with multiple services. Key Requirements: - Install and configure CentOS on a server - Set up Nginx as the web server - Configure the server to also function as a database and file server - Ensure the server is secure and optimized for performance - Provide documentation of the setup and configuration for future reference.

I'm in need of a website similar to , built on WordPress. The website should come with a user-friendly management console that enables me to edit articles, create new website sections, and manage user accounts. I'm looking for a freelancer who can also provide a Zoom meeting to guide me through using the various features of the console. Key requirements include: - **Customizable Management Console**: The console should allow me to perform tasks such as editing existing articles, creating new website sections, and managing user accounts. - **Design Preferences**: Incorporate a custom logo and colors, ensuring a modern and clean design. - **Training and Support**: I would like a one-on-one Zoom session for understanding the console's full capabilities and how to use them eff...

I'm looking for a skilled developer to create a user-friendly website for my MMORPG game server. Key elements of the project include: - Designing an engaging and intuitive UX/UI template for the website that resonates with the game's theme and aesthetics - Inclusion of essential features to enhance user experience Your expertise in web development, specifically in the gaming sector, will be crucial to this project's success. A strong understanding of user behavior, and the ability to translate that into a visually appealing and functional website is a must. Please provide a portfolio showcasing your previous work in this area. Experience with MMORPGs or gaming websites will be highly valued.

I need a Cloudflare expert to set up and configure my server for a high traffic website. - Tasks: The primary task will be setting up and configuring the server for the website. This includes but is not limited to ensuring the server is set up correctly, testing its performance and functionality, and making any necessary adjustments. - Specific Optimization: Experience in optimizing servers for high traffic websites is a must. - Cloudflare Specifics: While the primary focus is on server setup, knowledge of Cloudflare and its CDN (Content Delivery Network) feature is highly desired. Ideal Freelancer: A Cloudflare expert with experience in server setup and optimization, particularly for high traffic websites. Knowledge of setting up and configuring ...

Hi, I am looking for expert to connect SQL database togoogle looker studio so we can analise data and creat reports, it is a long term coopartion. Please provide implementation cost and hourly charge. Best.

...programmer who is well-versed in SQL Server 2019. The primary task is to ensure that new columns added to the database are correctly displayed in the Excel report generated by the application also fix some minor areas that will discuss in detail Key Responsibilities: - Troubleshoot and fix the issue of new columns not being displayed in the Excel report - Ensure that all relevant data is correctly fetched from the SQL Server 2019 database - Implement a seamless solution that does not affect the overall functionality of the application Ideal Skills and Experience: - Strong proficiency in C# programming language - Expert knowledge of SQL Server 2019, including stored procedures and functions - Prior experience with si...

I have nearly completed my CV, but I'm looking for a professional to help me redesign it. The aim is to create a more modern, minimalist, creative, and visually appealing layout. Key Requirements: - Tweak the content organization for maximum impact - Implement a professional and elegant font choice - Craft a layout that's ideal for job applications. Ideal Skills and Experience: - Proven track record in revamping CVs with a creative touch - Strong understanding of design principles and typography - Ability to tailor CVs for job applications. Please share relevant samples of your previous CV design work.

If you read it start your message with 'REACT'. I'm looking for a React specialist to help me deploy a wallet connect feature on my server. This is a React project that I need to deploy on my server. The project is for a wallet connect feature for crypto. There is already a working example from GitHub and I need it deployed on my server. Experience in the following areas would be ideal: - Proficiency in React - Experience with deploying projects on servers

...complete but due to some error while connecting to the database some code is missing and the connection is not completed. You have to find out where the problem is and fix it properly. I will help you in everything ******* I'm seeking a skilled PHP developer to assist with a project that involves fixing a PHP file and combining a Php ,MySQL database. The main tasks for this project include: - Resolving a database connection issue in the PHP file. - Combining the MySQL database in the backend of the PHP file. Your role will be crucial in ensuring that the database is correctly integrated into the PHP file and that the database connection is stable and error-free. The PHP file should be able to successfully communicate with the MySQL ...

We are in the final stage of migrating an existing Django Project to a new machine in a docker compose stack. The database is already moved over. We are stuck with python dependency issues. You need to have good knowledge in - Django and Python3 - Docker, especially Compose stacks - Postgresql You will be working with a system admin who is in the middle of the migration and take over the dependency part, tmate will be used to work together. If you have read this, please add "HDJX34K" to your bid or it will be considered spam, ignored and removed. Your job: - docker compose build - have a look at the python dependency issues - try to resolve them and rebuild. - eventually adjust Django's accordingly. We want this work done now, and you must be able to start immed...

App para elaborar presupuestos fuera de la tienda. actualmente tengo un sistema de escritorio elaborado en sql server para facturacion. El sistema Funciona perfecto y tiene la opción de realizar cotizaciones pero quiero incorporar una app para realizar las cotizaciones de los clientes foráneos ya que tengo un empleado que los visita semanalmente y me toca estar transcribiendo los pedidos. Seria una app que permita cargar los inventarios y los clientes al momento de estar en la tienda Y luego poder realizar los pedidos o cotizaciones offline cuando se este fuera. Para luego cuando llegue a la tienda hacer la actualización o descarga de pedidos. que tan dificil es hacer la app para android y para ios.

...legal professionals. The project includes creating both a web application and a mobile application for service providers. Responsibilities:Design and develop an intuitive user interface for three distinct profiles: clients (bailiffs), service providers (drivers, couriers, movers, locksmiths), and administrators. Integrate a real-time booking system with calendar and availability management. Implement secure payment systems and automatic notification features. Ensure compatibility between the web and mobile to best practices for security and data protection. Required Skills:Proven experience in web and mobile in front-end and back-end technologies (e.g., React, Node.js).Experience with SQL or NoSQL understanding of UX/UI design principles