New contrastive-learning methods for better data representation

New loss functions enable better approximation of the optimal loss and more-useful representations of multimodal data.

Many recent advances in artificial intelligence are the result of representation learning: a machine learning model learns to represent data items as vectors in a multidimensional space, where geometric relationships between vectors correspond to semantic relationships between items.

The M5 team at Amazon strives to construct general-purpose semantic representations of data related to the Amazon Store — product descriptions, queries, reviews, and more — that can be employed by machine learning (ML) systems throughout Amazon. Our approach involves leveraging all accessible data for each entity, often spanning multiple modalities.

One of the most successful ways to produce general-purpose representations is through contrastive learning, in which a model is trained on pairs of inputs, which are either positive (similar inputs/products) or negative (dissimilar inputs/products). The model learns to pull positive examples together and push negative examples apart.

Related content
Four CVPR papers from Prime Video examine a broad set of topics related to efficient model training for understanding and synthesizing long-form cinematic content.

In a pair of recent papers, M5 researchers have made substantial contributions to the theory and practice of contrastive learning. In “Why do we need large batch sizes in contrastive learning? A gradient-bias perspective”, presented at the 2022 Neural Information Processing Systems (NeurIPS) conference, we propose a new contrastive-learning loss function that enables models to converge on useful representations with lower memory cost and less training data.

And in “Understanding and constructing latent modality structures in multi-modal representation learning”, presented at this year’s Computer Vision and Pattern Recognition conference (CVPR), we propose geometric constraints on the representations of different modes of the same data item — say, image and text — that are more useful for downstream tasks than simply trying to resolve both representations to the same point in the representational space.

Do we need large batch sizes in contrastive learning?

In contrast with standard ML methods, contrastive learning typically requires very large batch sizes to achieve good performance: several popular models, for instance, require tens of thousands of training examples, significantly increasing the memory overhead; reducing the batch size can impair performance. In our NeurIPS paper, we attempt to understand this phenomenon and to propose techniques for mitigating it.

Related content
Two methods presented at CVPR achieve state-of-the-art results by imposing additional structure on the representational space.

Part of the appeal of contrastive learning is that it’s unsupervised, meaning it doesn’t require data annotation. Positive pairs can be generated by mathematically transforming an “anchor sample” and pairing the transformed version with the original; negative pairs can be generated by pairing an anchor sample with transformed versions of other anchor samples. With image data, a transformation might involve re-cropping, reversing, or distorting the colors of the anchor sample; with textual data, a transformation might involve substituting synonyms for the words in a sentence.

Given a measure of similarity between vectors in the representational space, the standard loss function for contrastive learning involves a ratio whose numerator includes the similarity between an anchor sample and one of its transformations; the denominator includes the sum of the similarities of the anchor sample and all possible negative samples. The goal of training is to maximize that ratio.

In principle, given the possibility of applying transformations to negative samples, “all possible negative samples” could describe an infinite set. In practice, contrastive learning typically just relies on the negative examples available in the training batch. Hence the need for large batch sizes — to approximate an infinite sum.

contrastive_learning [Read-Only].png
The contrastive-learning framework. Approximating an infinite sum with the samples in a finite minibatch of training data can introduce gradient bias.

If the distribution of minibatch samples differs from the distribution of possible negatives, however, this approximation can bias the model. One difficulty in correcting the bias is that, because the loss function contrasts each positive pair with all possible negatives at once, in a ratio, it cannot be decomposed into a sum of sub-losses.

We address the decomposability problem using Bayesian augmentation. The general approach is that, for each anchor sample, we create a random auxiliary variable, which can be thought of as a weight applied to the anchor sample’s similarity scores. Using identity under the gamma function, we can show that the auxiliary variable follows a gamma distribution, which is easy to sample. As a consequence, we can rewrite the loss in an exponential rather than a fractional form, making it decomposable.

During training, we begin by sampling the auxiliary variables for the current batch of data from a gamma distribution, giving us the weight of the similarity scores for all the anchor samples. Conditioned on the sampled values, we then apply maximum likelihood estimation to optimize the parameters of the model, which will consider the sampled weights on the similarity scores from the first step. We then repeat this process for the entire dataset, summing a sequence of (weighted) sub-losses to produce a cumulative loss. In our paper, we show that this procedure will converge toward the expected loss for the original contrastive-loss function, with its infinite sum in the denominator.

Contrastive-learning losses.png
Results of 10 training runs on synthetic data with added noise, comparing a model trained with our decomposable loss function (red) to one trained with the conventional loss function (blue). With our loss, the model consistently converged to the optimum (1.0), while with the conventional loss, it never did.

We evaluate our approach through a number of experiments. In one, we used simulated data, into which we injected noise to simulate bias. Then we used both our loss and the conventional loss function to train a model 10 times, with different initialization values. At heavy noise levels, the model trained with the conventional loss failed to converge, while ours consistently converged to the optimum.

We also evaluated the models on a variety of downstream tasks, including zero-/few-shot image classification and image/text retrieval. Our approach showed significant performance improvement over state-of-the-art baseline methods.

What geometries work best for multimodal representation matching?

At M5, we are building scalable models that can handle multimodal data — for instance, multilingual models that translate between product descriptions in different languages or multi-entity models that jointly model different images of the same product. Contrastive learning is a promising method for building such models: data in different modalities that are associated with the same products can be treated as positive pairs, and contrastive learning pulls them together in the representational space.

Related content
A new metric-learning loss function groups together superclasses and learns commonalities within them.

We theoretically investigated whether the standard contrastive-learning framework is optimal in terms of the prediction error rate on downstream tasks, and the surprising answer is no. In our CVPR paper, we prove that if the information gap between two modalities is large — that is, if you can’t infer much about one modality from the other — then the best prediction error we can hope to achieve using standard contrastive-learning representations is larger than that we can achieve if we simply train a machine learning model directly on data in a single modality.

This makes some intuitive sense. Ideally, contrastive learning would pull the different modalities so tightly together that they would essentially resolve to a single point in the representational space. But of course, the reason to use multimodal representations for downstream tasks is that each modality may capture useful information that the other does not. Collapsing the different modalities’ representations together neutralizes this advantage.

Consequently, in our CVPR paper, we explore different geometrical relationships in the representational space that can establish correlations between multimodal data without sacrificing information specific to each mode. We propose three general approaches to constructing modality structures in the representational space, suited to intramodal representation, intermodal representation, and a combination of the two:

  1. a deep feature separation loss for intramodality regularization, which uses two types of neural network components to separate different modality information: one component captures information that’s shared between modalities (tuned according to the standard contrastive-learning loss), and the other, which is orthogonal to the first, captures information unique to the modality;
  2. a “Brownian-bridge” loss for intermodality regularization, which uses Brownian motion to plot several trajectories/transitions between the representation of one modality (say, text) and the other (say, an image) and constrains representations of augmented data to lie along one of those paths; and
  3. a geometric-consistency loss for both intra- and intermodality regularization, which enforces symmetry in the geometric relationships between representations in one modality and the corresponding representations in the other modality, while simultaneously enforcing symmetries in cross-modal geometric relationships.
Contrastive learning.png
Three types of modality structures that can improve modality representation learning for downstream tasks. (1) With deep feature separation, a model produces two orthogonal vectors for each modality, one that encodes information shared across modalities and one that encodes mode-specific information. (2) Brownian bridges use Brownian motion to generate trajectories/transitions between representations of data in different modes, defining a subspace in which the representations of augmented data are induced to lie. (3) Geometric consistency enforces symmetries in the relationships between data representations, both within modes (orange-orange and blue-blue) and across modes (blue-orange).

We have conducted extensive experiments on two popular multimodal representation-learning frameworks, the CLIP-based two-tower model and the ALBEF-based fusion model. We tested our model on a variety of tasks, including zero-/few-shot image classification, image-text retrieval, visual question answering, visual reasoning, and visual entailment. Our method achieves consistent improvements over existing methods, demonstrating the effectiveness and generalizability of our proposed approach on multimodal representation learning.

Going forward

Our NeurIPS and CVPR papers represent only two interesting projects from our M5 team. There is a lot more research on multimodal learning going on in M5. This includes generative models for images, videos, and text (e.g. Stable Diffusion, DreamBooth) to enable data synthesis and representation learning and training and applying large language models to enhance customer shopping experiences. We expect to report on more research highlights in the near future.

Research areas

Related content

GB, MLN, Edinburgh
We’re looking for a Machine Learning Scientist in the Personalization team for our Edinburgh office experienced in generative AI and large models. You will be responsible for developing and disseminating customer-facing personalized recommendation models. This is a hands-on role with global impact working with a team of world-class engineers and scientists across the Edinburgh offices and wider organization. You will lead the design of machine learning models that scale to very large quantities of data, and serve high-scale low-latency recommendations to all customers worldwide. You will embody scientific rigor, designing and executing experiments to demonstrate the technical efficacy and business value of your methods. You will work alongside a science team to delight customers by aiding in recommendations relevancy, and raise the profile of Amazon as a global leader in machine learning and personalization. Successful candidates will have strong technical ability, focus on customers by applying a customer-first approach, excellent teamwork and communication skills, and a motivation to achieve results in a fast-paced environment. Our position offers exceptional opportunities for every candidate to grow their technical and non-technical skills. If you are selected, you have the opportunity to make a difference to our business by designing and building state of the art machine learning systems on big data, leveraging Amazon’s vast computing resources (AWS), working on exciting and challenging projects, and delivering meaningful results to customers world-wide. Key job responsibilities Develop machine learning algorithms for high-scale recommendations problems. Rapidly design, prototype and test many possible hypotheses in a high-ambiguity environment, making use of both quantitative analysis and business judgement. Collaborate with software engineers to integrate successful experimental results into large-scale, highly complex Amazon production systems capable of handling 100,000s of transactions per second at low latency. Report results in a manner which is both statistically rigorous and compellingly relevant, exemplifying good scientific practice in a business environment.
IN, TS, Hyderabad
Welcome to the Worldwide Returns & ReCommerce team (WWR&R) at Amazon.com. WWR&R is an agile, innovative organization dedicated to ‘making zero happen’ to benefit our customers, our company, and the environment. Our goal is to achieve the three zeroes: zero cost of returns, zero waste, and zero defects. We do this by developing products and driving truly innovative operational excellence to help customers keep what they buy, recover returned and damaged product value, keep thousands of tons of waste from landfills, and create the best customer returns experience in the world. We have an eye to the future – we create long-term value at Amazon by focusing not just on the bottom line, but on the planet. We are building the most sustainable re-use channel we can by driving multiple aspects of the Circular Economy for Amazon – Returns & ReCommerce. Amazon WWR&R is comprised of business, product, operational, program, software engineering and data teams that manage the life of a returned or damaged product from a customer to the warehouse and on to its next best use. Our work is broad and deep: we train machine learning models to automate routing and find signals to optimize re-use; we invent new channels to give products a second life; we develop highly respected product support to help customers love what they buy; we pilot smarter product evaluations; we work from the customer backward to find ways to make the return experience remarkably delightful and easy; and we do it all while scrutinizing our business with laser focus. You will help create everything from customer-facing and vendor-facing websites to the internal software and tools behind the reverse-logistics process. You can develop scalable, high-availability solutions to solve complex and broad business problems. We are a group that has fun at work while driving incredible customer, business, and environmental impact. We are backed by a strong leadership group dedicated to operational excellence that empowers a reasonable work-life balance. As an established, experienced team, we offer the scope and support needed for substantial career growth. Amazon is earth’s most customer-centric company and through WWR&R, the earth is our customer too. Come join us and innovate with the Amazon Worldwide Returns & ReCommerce team!
US, CA, Palo Alto
Amazon’s Advertising Technology team builds the technology infrastructure and ad serving systems to manage billions of advertising queries every day. The result is better quality advertising for publishers and more relevant ads for customers. In this organization you’ll experience the benefits of working in a dynamic, entrepreneurial environment, while leveraging the resources of Amazon.com (AMZN), one of the world's leading companies. Amazon Publisher Services (APS) helps publishers of all sizes and on all channels better monetize their content through effective advertising. APS unites publishers with advertisers across devices and media channels. We work with Amazon teams across the globe to solve complex problems for our customers. The end results are Amazon products that let publishers focus on what they do best - publishing. The APS Publisher Products Engineering team is responsible for building cloud-based advertising technology services that help Web, Mobile, Streaming TV broadcasters and Audio publishers grow their business. The engineering team focuses on unlocking our ad tech on the most impactful Desktop, mobile and Connected TV devices in the home, bringing real-time capabilities to this medium for the first time. As a successful Data Scientist in our team, · You are an analytical problem solver who enjoys diving into data, is excited about investigations and algorithms, and can credibly interface between technical teams and business stakeholders. You will collaborate directly with product managers, BIEs and our data infra team. · You will analyze large amounts of business data, automate and scale the analysis, and develop metrics (e.g., user recognition, ROAS, Share of Wallet) that will enable us to continually measure the impact of our initiatives and refine the product strategy. · Your analytical abilities, business understanding, and technical aptitude will be used to identify specific and actionable opportunities to solve existing business problems and look around corners for future opportunities. Your expertise in synthesizing and communicating insights and recommendations to audiences of varying levels of technical sophistication will enable you to answer specific business questions and innovate for the future. · You will have direct exposure to senior leadership as we communicate results and provide scientific guidance to the business. Major responsibilities include: · Utilizing code (Apache, Spark, Python, R, Scala, etc.) for analyzing data and building statistical models to solve specific business problems. · Collaborate with product, BIEs, software developers, and business leaders to define product requirements and provide analytical support · Build customer-facing reporting to provide insights and metrics which track system performance · Influence the product strategy directly through your analytical insights · Communicating verbally and in writing to business customers and leadership team with various levels of technical knowledge, educating them about our systems, as well as sharing insights and recommendations
US, WA, Seattle
Prime Video is a first-stop entertainment destination offering customers a vast collection of premium programming in one app available across thousands of devices. Prime members can customize their viewing experience and find their favorite movies, series, documentaries, and live sports – including Amazon MGM Studios-produced series and movies; licensed fan favorites; and programming from Prime Video add-on subscriptions such as Apple TV+, Max, Crunchyroll and MGM+. All customers, regardless of whether they have a Prime membership or not, can rent or buy titles via the Prime Video Store, and can enjoy even more content for free with ads. Are you interested in shaping the future of entertainment? Prime Video's technology teams are creating best-in-class digital video experience. As a Prime Video technologist, you’ll have end-to-end ownership of the product, user experience, design, and technology required to deliver state-of-the-art experiences for our customers. You’ll get to work on projects that are fast-paced, challenging, and varied. You’ll also be able to experiment with new possibilities, take risks, and collaborate with remarkable people. We’ll look for you to bring your diverse perspectives, ideas, and skill-sets to make Prime Video even better for our customers. With global opportunities for talented technologists, you can decide where a career Prime Video Tech takes you! In Prime Video READI, our mission is to automate infrastructure scaling and operational readiness. We are growing a team specialized in time series modeling, forecasting, and release safety. This team will invent and develop algorithms for forecasting multi-dimensional related time series. The team will develop forecasts on key business dimensions with optimization recommendations related to performance and efficiency opportunities across our global software environment. As a founding member of the core team, you will apply your deep coding, modeling and statistical knowledge to concrete problems that have broad cross-organizational, global, and technology impact. Your work will focus on retrieving, cleansing and preparing large scale datasets, training and evaluating models and deploying them to production where we continuously monitor and evaluate. You will work on large engineering efforts that solve significantly complex problems facing global customers. You will be trusted to operate with complete independence and are often assigned to focus on areas where the business and/or architectural strategy has not yet been defined. You must be equally comfortable digging in to business requirements as you are drilling into design with development teams and developing production ready learning models. You consistently bring strong, data-driven business and technical judgment to decisions. You will work with internal and external stakeholders, cross-functional partners, and end-users around the world at all levels. Our team makes a big impact because nothing is more important to us than delivering for our customers, continually earning their trust, and thinking long term. You are empowered to bring new technologies to your solutions. If you crave a sense of ownership, this is the place to be.
US, WA, Seattle
Amazon Advertising operates at the intersection of eCommerce and advertising, and is investing heavily in building a world-class advertising business. We are defining and delivering a collection of self-service performance advertising products that drive discovery and sales. Our products are strategically important to our Retail and Marketplace businesses driving long-term growth. We deliver billions of ad impressions and millions of clicks daily and are breaking fresh ground to create world-class products to improve both shopper and advertiser experience. With a broad mandate to experiment and innovate, we grow at an unprecedented rate with a seemingly endless range of new opportunities. The Ad Response Prediction team in Sponsored Products organization build advanced deep-learning models, large-scale machine-learning pipelines, and real-time serving infra to match shoppers’ intent to relevant ads on all devices, for all contexts and in all marketplaces. Through precise estimation of shoppers’ interaction with ads and their long-term value, we aim to drive optimal ads allocation and pricing, and help to deliver a relevant, engaging and delightful ads experience to Amazon shoppers. As the business and the complexity of various new initiatives we take continues to grow, we are looking for talented Applied Scientists to join the team. Key job responsibilities As a Applied Scientist II, you will: * Conduct hands-on data analysis, build large-scale machine-learning models and pipelines * Work closely with software engineers on detailed requirements, technical designs and implementation of end-to-end solutions in production * Run regular A/B experiments, gather data, perform statistical analysis, and communicate the impact to senior management * Establish scalable, efficient, automated processes for large-scale data analysis, machine-learning model development, model validation and serving * Provide technical leadership, research new machine learning approaches to drive continued scientific innovation * Be a member of the Amazon-wide Machine Learning Community, participating in internal and external MeetUps, Hackathons and Conferences
US, WA, Bellevue
mmPROS Surface Research Science seeks an exceptional Applied Scientist with expertise in optimization and machine learning to optimize Amazon's middle mile transportation network, the backbone of its logistics operations. Amazon's middle mile transportation network utilizes a fleet of semi-trucks, trains, and airplanes to transport millions of packages and other freight between warehouses, vendor facilities, and customers, on time and at low cost. The Surface Research Science team delivers innovation, models, algorithms, and other scientific solutions to efficiently plan and operate the middle mile surface (truck and rail) transportation network. The team focuses on large-scale problems in vehicle route planning, capacity procurement, network design, forecasting, and equipment re-balancing. Your role will be to build innovative optimization and machine learning models to improve driver routing and procurement efficiency. Your models will impact business decisions worth billions of dollars and improve the delivery experience for millions of customers. You will operate as part of a team of innovative, experienced scientists working on optimization and machine learning. You will work in close collaboration with partners across product, engineering, business intelligence, and operations. Key job responsibilities - Design and develop optimization and machine learning models to inform our hardest planning decisions. - Implement models and algorithms in Amazon's production software. - Lead and partner with product, engineering, and operations teams to drive modeling and technical design for complex business problems. - Lead complex modeling and data analyses to aid management in making key business decisions and set new policies. - Write documentation for scientific and business audiences. About the team This role is part of mmPROS Surface Research Science. Our mission is to build the most efficient and optimal transportation network on the planet, using our science and technology as our biggest advantage. We leverage technologies in optimization, operations research, and machine learning to grow our businesses and solve Amazon's unique logistical challenges. Scientists in the team work in close collaboration with each other and with partners across product, software engineering, business intelligence, and operations. They regularly interact with software engineering teams and business leadership.
IL, Tel Aviv
Come join the AWS Agentic AI science team in building the next generation models for intelligent automation. AWS, the world-leading provider of cloud services, has fostered the creation and growth of countless new businesses, and is a positive force for good. Our customers bring problems that will give Applied Scientists like you endless opportunities to see your research have a positive and immediate impact in the world. You will have the opportunity to partner with technology and business teams to solve real-world problems, have access to virtually endless data and computational resources, and to world-class engineers and developers that can help bring your ideas into the world. As part of the team, we expect that you will develop innovative solutions to hard problems, and publish your findings at peer reviewed conferences and workshops. We are looking for world class researchers with experience in one or more of the following areas - autonomous agents, API orchestration, Planning, large multimodal models (especially vision-language models), reinforcement learning (RL) and sequential decision making. Key job responsibilities PhD, or Master's degree and 4+ years of CS, CE, ML or related field experience 3+ years of building models for business application experience Experience in patents or publications at top-tier peer-reviewed conferences or journals Experience programming in Java, C++, Python or related language Experience in any of the following areas: algorithms and data structures, parsing, numerical optimization, data mining, parallel and distributed computing, high-performance computing
IL, Haifa
Come join the AWS Agentic AI science team in building the next generation models for intelligent automation. AWS, the world-leading provider of cloud services, has fostered the creation and growth of countless new businesses, and is a positive force for good. Our customers bring problems that will give Applied Scientists like you endless opportunities to see your research have a positive and immediate impact in the world. You will have the opportunity to partner with technology and business teams to solve real-world problems, have access to virtually endless data and computational resources, and to world-class engineers and developers that can help bring your ideas into the world. As part of the team, we expect that you will develop innovative solutions to hard problems, and publish your findings at peer reviewed conferences and workshops. We are looking for world class researchers with experience in one or more of the following areas - autonomous agents, API orchestration, Planning, large multimodal models (especially vision-language models), reinforcement learning (RL) and sequential decision making.
US, MA, Westborough
We are seeking a Principal Applied Scientist to lead the development of our autonomous driving stack for last-mile delivery vehicles. In this role, you will drive technical innovation, architect advanced autonomous systems, and lead a team of researchers and engineers in pushing the boundaries of what's possible in autonomous delivery. Key job responsibilities As the Principal Applied Scientist, you will architect and evolve LMDA's autonomous driving stack for last-mile delivery vehicles. Your role involves driving research and development in key areas such as perception, prediction, planning, and control. You will develop novel algorithms and approaches to solve complex challenges in urban autonomous navigation. A critical aspect of your role will be leading system-level architecture decisions and setting technical direction for the autonomous systems team. You will mentor and develop a team of scientists and engineers, fostering a culture of innovation and excellence. This involves close collaboration with cross-functional teams including hardware, safety, and operations to ensure seamless integration of autonomous systems. As a senior technical leader, you will represent LMDA's technical capabilities to partners, customers, and at industry conferences. In this role, you will define and execute the technical roadmap for LMDA's autonomous systems. This includes identifying key research areas and technological advancements that will drive LMDA's competitive advantage. A crucial aspect of your role will be balancing long-term research goals with near-term product delivery needs. You will lead the integration of various autonomous subsystems into a cohesive, performant stack. This includes developing and implementing strategies for optimizing system performance across hardware and software. You will also design and oversee testing and validation frameworks for autonomous systems. About the team Last Mile Delivery Automation (LMDA) is at the forefront of revolutionizing the logistics industry through advanced autonomous vehicle technology. Our mission is to create safe, efficient, and scalable autonomous solutions for last-mile delivery, reducing costs and environmental impact while improving delivery speed and reliability.
US, VA, Arlington
he WWGST (Worldwide Grocery Stores Tech) teams are seeking a highly motivated Senior Research Scientist (Level 6) to join our team that is focused on building new technologies for grocery stores. We are a team of applied scientists invent new algorithms (especially artificial intelligence, computer vision and sensor fusion) to improve customer experiences in grocery shopping such as Dash Cart or Self-CheckOut. The Amazon Dash Cart is a smart shopping cart that uses sensors to keep track of what a shopper has added. Once done, they can bypass the checkout lane and just walk out. The cart comes with convenience features like a store map, a basket that can weigh produce, and product recommendations. Amazon Dash Cart’s are available at Amazon Fresh, Whole Foods. Learn more about the Dash Cart at https://www.amazon.com/b?ie=UTF8&node=21289116011 Key job responsibilities As a Senior Research Scientist, you will help solve a variety of technical challenges and mentor other junior scientists. You will be leader of the science team to resolve the hard problems. You will play an active role in translating business and functional requirements into concrete deliverables and build quick prototypes or proofs of concept in partnership with other technology leaders within the team. You will tackle challenging, novel situations every day and given the size of this initiative, you’ll have the opportunity to work with multiple technical teams at Amazon in different locations. You should be comfortable with a degree of ambiguity that’s higher than most projects and relish the idea of solving problems that, frankly, haven’t been solved before - anywhere. Along the way, we guarantee that you’ll learn a ton, have fun and make a positive impact on millions of people. About the team Diverse Experiences Amazon values diverse experiences. Even if you do not meet all of the preferred qualifications and skills listed in the job description, we encourage candidates to apply. If your career is just starting, hasn’t followed a traditional path, or includes alternative experiences, don’t let it stop you from applying. Work/Life Balance We value work-life harmony. Achieving success at work should never come at the expense of sacrifices at home, which is why flexible work hours and arrangements are part of our culture. When we feel supported in the workplace and at home, there’s nothing we can’t achieve in the cloud. Mentorship and Career Growth We’re continuously raising our performance bar as we strive to become Earth’s Best Employer. That’s why you’ll find endless knowledge-sharing, mentorship and other career-advancing resources here to help you develop into a better-rounded professional.