Glossary
20 terms
BM25
The production-grade evolution of TF-IDF: adds term-frequency saturation and document-length normalization. Still the default ranking function inside Elasticsearch and OpenSearch.
CNN
Convolutional neural network. Learns local filters that slide across the input, exploiting spatial structure. The default shape for images before Vision Transformers arrived.
Constrained decoding
Restricting which tokens can be sampled at each step, with a grammar or schema, so the output is guaranteed to be well-formed.
Dense embeddings
Vector representations from a transformer encoder. The same word gets a different vector depending on context, so semantically related phrases land close together in vector space even with zero shared words.
Google ADK
Google's agent framework: tightest integration with Gemini and Vertex AI, native support for the Agent-to-Agent (A2A) protocol.
Greedy decoding
Greedy decoding: picking the single highest-probability token at every step, with no search over alternative paths.
Harness
The fixed scaffolding that runs a system against a set of cases and reports the result: it owns the inputs, the invocation, and the scoring, so the same run is repeatable. An eval harness is the specific case for a generative system: frozen inputs, a scorer for each property, and a pass rate.
Hybrid search + reranking
Run lexical (BM25) and dense embeddings in parallel, merge the rankings (often via reciprocal rank fusion), then optionally rerank the top candidates with a cross-encoder that scores the query and candidate jointly.
LangGraph
The most enterprise-adopted stateful agent orchestration framework, from the LangChain team.
Logits
A model’s raw, unnormalized scores for each candidate token, before the softmax turns them into a probability distribution.
Mixture-of-experts
A layer made of several parallel sub-networks, the experts, plus a router that sends each token to only a few of them. Total parameter count grows while inference cost stays close to that of a much smaller model.
Pydantic AI / Pydantic Graph
A typed agent SDK from the Pydantic team. Pydantic Graph specifically is a typed graph-workflow builder (BaseNode, GraphRunContext, End) for modeling routing and state-machine logic.
Pydantic model
A Python class (subclass of BaseModel) that defines a data shape via type hints, then validates and parses input against it at runtime instead of trusting an untyped dict.
RNN
Recurrent neural network. Processes a sequence one step at a time, carrying a hidden state forward. Stepping through that state sequentially is hard to parallelize, part of why attention displaced it.
Softmax
The function that turns a vector of logits into a probability distribution: exponentiate each score and divide by the sum, so the outputs are positive and add to 1.
State-space model
State-space model. Processes a sequence through a compressed, continuously updated state, built for the parallel training and long-context efficiency that made Transformers dominant. Mamba is a current example.
Temperature
A scalar that rescales a model’s logits before the softmax. Values below 1 sharpen the distribution toward the top tokens; values above 1 flatten it toward the tail.
TF-IDF
Term Frequency, Inverse Document Frequency: weights a word by how often it appears in one document versus how rare it is across the whole corpus. Sparse and lexical, no notion of meaning.
Top-p (nucleus sampling)
Nucleus sampling. Sorts tokens by probability and samples from the smallest set whose cumulative mass passes a threshold p, so the pool size adapts to the shape of the distribution instead of staying fixed.
Transformer
The architecture built on self-attention (block 03). Every token attends to every other token in the window, computed in parallel rather than stepped through sequentially like an RNN.
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