A molecular structure can contain many segments, and inspecting them one by one is a slow way to answer a simple question: which segments are unusually long, or which ones deserve a closer look? In SAMSON, the Node Specification Language (NSL) lets you search segment nodes by properties such as their number of residues, structural groups, atoms, or elements. That turns a broad visual scan into a targeted first pass.
Start with the question you need to answer
If you are looking for long segments, begin with the residue count. The short form s.nr refers to segment.numberOfResidues. For example, s.nr > 100 matches segments with more than 100 residues. If you want to examine a narrower size band, use a range such as s.nr 100:120.
This is useful when a model contains many chains or other segments and you need to identify candidates for closer inspection. Rather than relying on how large a segment looks in a particular view, you can search using a count. The search does not tell you whether a segment is biologically important; it helps you find segments that meet the criterion you chose.
Use a second count to understand what you found
Residue count is only one way to describe a segment. The attribute s.nsg searches by number of structural groups. For example, s.nsg > 10 finds segments with more than 10 structural groups, while s.nsg 10:12 searches a range.
These counts answer different questions. A segment’s number of residues and number of structural groups are separate attributes; do not assume one is a substitute for the other. Checking both can help you describe a candidate more clearly and decide what to inspect next.
Check composition and scale
Segment searches can also use inherited structural-group attributes. For example, s.nat < 1000 searches by number of atoms, and s.nC < 10 searches by number of carbons. Similar count attributes are available for hydrogens, nitrogens, oxygens, sulfurs, and coarse-grained atoms. These can help when your question is about the scale or composition of a segment rather than its length.
For instance, a useful manual triage could be: first search for segments above a residue-count threshold; then inspect the candidates using a separate atom-count or element-count query. Treat each result as a filter for attention, not as an interpretation of the molecule. The criteria you choose depend on the structure and the question you are investigating.
Remember the segment scope
These expressions use the segment attribute space, whose short name is s. It matches segment nodes. Many available attributes are inherited from broader node or structural-group attribute spaces, so a segment query can refer to properties such as visibility, name, atom counts, and partial charge as well as segment-specific counts.
For a quick start, try s.nr > 100 when you need to locate longer segments, or s.nr 100:120 when you want a bounded range. Then choose another attribute based on what you need to learn about those candidates. Keeping the search question specific makes it easier to understand why a segment matched.
See the segment attribute reference for the complete list of attributes and examples.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.