| What it is | Rules, search and optimisation written by people, plus pre-trained AI services called through an API. | Statistical models trained on your structured data. | Many-layered neural networks trained on large or unstructured data, or a pre-trained foundation model. |
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| Data needs | Little or none of your own, beyond test samples and the rules themselves. | Hundreds to millions of labelled, tabular rows with history, depending on the problem. | Large labelled sets to train from scratch, or a modest labelled set to fine-tune a pre-trained model. Prompting and RAG need none for training. |
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| Compute | Low. Pay per request on managed services. | Moderate. CPU training is often enough, with scheduled retraining. | High for training and fine-tuning (GPUs or AI accelerators). Inference can also be heavy. |
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| Explainability | High for rules. Managed services return confidence scores but their internals are opaque. | Medium to high. Linear models and trees can be explained, and SHAP-style tools help with ensembles. | Low. Explanations are approximate, so evaluation, human review and monitoring carry more of the assurance. |
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| Typical algorithms and services | Decision tables, workflow rules, OCR and document AI (Amazon Textract), NLP APIs (Amazon Comprehend), Step Functions. | Linear and logistic regression, decision trees, random forests, gradient boosting (XGBoost), k-means, time-series models, on SageMaker AI. | CNNs, vision transformers, LSTMs, transformers and LLMs, on SageMaker AI, Amazon Rekognition Custom Labels or Amazon Bedrock. |
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| When to use it | The task is well defined, a managed service already does it, or decisions must be fully traceable. | You have good historical, structured data and need a prediction or score you can test and explain. | The input is images, audio or free text, patterns are too complex for features you can design, or you need generation. |
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