Storage Layout

This article is part of the Advanced User's Guide. It presents some low-level details on how data is stored in the database files.

Data Types

The following data types are used for specifying the storage layout:

Type	Description	Example (native → hex integers)
Num	Compressed integer (1-5 bytes), specified in Num.java	15 → 0F; 511 → 41 FF
Token	Length (Num) and bytes of UTF8 byte representation	Hello → 05 48 65 6c 6c 6f
Double	Number, stored as token	123 → 03 31 32 33
Boolean	Boolean (1 byte, 00 or 01)	true → 01
Nums, Tokens, Doubles	Arrays of values, introduced with the number of entries	1,2 → 02 01 31 01 32
TokenSet	Key array (Tokens), next/bucket/size arrays (3x Nums)

Database Files

The following tables illustrate the layout of the BaseX database files. All files are suffixed with .basex.

Meta Data, Name/Path/Doc Indexes: inf

Description	Format	Method
1. Meta Data	1. Key/value pairs, in no particular order (Token/Token):   • Examples: FNAME, TIME, SIZE, ...   • PERM → Number of users (Num), and name/password/permission values for each user (Token/Token/Num) 2. Empty key as finalizer	DiskData() MetaData() Users()
2. Main memory indexes	1. Key/value pairs, in no particular order (Token/Token):   • TAGS → Tag Index   • ATTS → Attribute Name Index   • PATH → Path Index   • NS → Namespaces   • DOCS → Document Index 2. Empty key as finalizer	DiskData()
2 a) Name Index Tag/attribute names	1. Token set, storing all names (TokenSet) 2. One StatsKey instance per entry: 2.1. Content kind (Num): 2.1.1. Number: min/max (Doubles) 2.1.2. Category: number of entries (Num), entries (Tokens) 2.2. Number of entries (Num) 2.3. Leaf flag (Boolean) 2.4. Maximum text length (Double; legacy, could be Num)	Names() TokenSet.read() StatsKey()
2 b) Path Index	1. Flag for path definition (Boolean, always true; legacy) 2. PathNode: 2.1. Name reference (Num) 2.2. Node kind (Num) 2.3. Number of occurrences (Num) 2.4. Number of children (Num) 2.5. Double; legacy, can be reused or discarded 2.6. Recursive generation of child nodes (→ 2)	PathSummary() PathNode()
2 c) Namespaces	1. Token set, storing prefixes (TokenSet) 2. Token set, storing URIs (TokenSet) 3. NSNode: 3.1. pre value (Num) 3.2. References to prefix/URI pairs (Nums) 3.3. Number of children (Num) 3.4. Recursive generation of child nodes (→ 3)	Namespaces() NSNode()
2 d) Document Index	Array of integers, representing the distances between all document pre values (Nums)	DocIndex()

Node Table: tbl, tbli

• tbl: Main database table, stored in blocks.
• tbli: Database directory, organizing the database blocks.

Some more information on the Node table storage is available.

Texts: txt, atv

• txt: Heap file for text values (document names, string values of texts, comments and processing instructions)
• atv: Heap file for attribute values.

Value Indexes: txtl, txtr, atvl, atvr

Text Index:

• txtl: Heap file with ID lists.
• txtr: Index file with references to ID lists.

The Attribute Index is contained in the files atvl and atvr; it uses the same layout.

Full-Text Fuzzy Index: ftxx, ftxy, ftxz

...will soon be reimplemented.

Full-Text Trie Index: ftxa, ftxb, ftxc

...will soon be dismissed.