[doc] re-org api doc page (#6742)

docs/source/api/python/dgl.graphbolt.rst

@@ -5,53 +5,192 @@
 
 .. currentmodule:: dgl.graphbolt
 
-**dgl.graphbolt** is a dataloading framework for GNN that provides well-defined APIs for each stage of the data pipeline and multiple standard implementations.
+**dgl.graphbolt** is a dataloading framework for GNN that provides well-defined
+APIs for each stage of the data pipeline and multiple standard implementations.
 
-APIs
--------------------------
+Dataset
+-------
+
+A dataset is a collection of graph structure data, feature data and tasks.
 
 .. autosummary::
     :toctree: ../../generated/
     :nosignatures:
     :template: graphbolt_classtemplate.rst
 
-    DataLoader
     Dataset
+    OnDiskDataset
+    BuiltinDataset
+    LegacyDataset
     Task
+
+Graph
+-----
+
+A graph is a collection of nodes and edges. It can be a homogeneous graph or a
+heterogeneous graph.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    SamplingGraph
+    FusedCSCSamplingGraph
+
+
+Feature and FeatureStore
+------------------------
+
+A feature is a collection of data(tensor, array). A feature store is a
+collection of features.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    Feature
+    FeatureStore
+    BasicFeatureStore
+    TorchBasedFeature
+    TorchBasedFeatureStore
+    GPUCachedFeature
+
+
+DataLoader
+----------
+
+A dataloader is for iterating over a dataset and generate mini-batches.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    DataLoader
+
+
+ItemSet
+-------
+
+An item set is a iterable collection of items.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
     ItemSet
     ItemSetDict
+
+
+ItemSampler
+-----------
+
+An item sampler is for sampling items from an item set.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
     ItemSampler
     DistributedItemSampler
-    NegativeSampler
-    SubgraphSampler
-    SampledSubgraph
-    SamplingGraph
+
+
+MiniBatch
+---------
+
+A mini-batch is a collection of sampled subgraphs and their corresponding
+features. It is the basic unit for training a GNN model.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
     MiniBatch
-    MiniBatchTransformer
     DGLMiniBatch
     DGLMiniBatchConverter
-    Feature
-    FeatureStore
-    FeatureFetcher
-    CopyTo
 
 
-Standard Implementations
--------------------------
+NegativeSampler
+---------------
+
+A negative sampler is for sampling negative items from mini-batches.
 
 .. autosummary::
     :toctree: ../../generated/
     :nosignatures:
     :template: graphbolt_classtemplate.rst
 
-    OnDiskDataset
-    BuiltinDataset
-    FusedCSCSamplingGraph
+    MiniBatchTransformer
+    NegativeSampler
     UniformNegativeSampler
+
+
+SubgraphSampler
+---------------
+
+A subgraph sampler is for sampling subgraphs from a graph.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    SubgraphSampler
+    SampledSubgraph
     NeighborSampler
     LayerNeighborSampler
+    SampledSubgraphImpl
     FusedSampledSubgraphImpl
-    BasicFeatureStore
-    TorchBasedFeature
-    TorchBasedFeatureStore
-    GPUCachedFeature
+    InSubgraphSampler
+
+
+FeatureFetcher
+--------------
+
+A feature fetcher is for fetching features from a feature store.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    FeatureFetcher
+
+
+CopyTo
+------
+
+This datapipe is for copying data to a device.
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+    :template: graphbolt_classtemplate.rst
+
+    CopyTo
+
+
+Utilities
+---------
+
+.. autosummary::
+    :toctree: ../../generated/
+    :nosignatures:
+
+    fused_csc_sampling_graph
+    load_from_shared_memory
+    from_dglgraph
+    etype_str_to_tuple
+    etype_tuple_to_str
+    add_reverse_edges
+    exclude_seed_edges
+    compact_csc_format
+    unique_and_compact
+    unique_and_compact_csc_formats
+    unique_and_compact_node_pairs
+