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1、BRITISH STANDARD BS 7567-2: 1992 Incorporating Amendment No. 1 Electronic transfer of geographic information (NTF) Part 2: Specification for implementing plain NTF Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BS
2、I BS 7567-2:1992 This British Standard, having been prepared under the direction of the Information Systems Technology Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 May 1992 BSI 09-1999 The following BSI references relate to the work
3、 on this standard: Committee reference IST/36 Draft for comment 91/65602 DC ISBN 0 580 20875 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Information Systems Technology Standards Policy Committee (IST/-) to Technical Committee IST/3
4、6, upon which the following bodies were represented: Advanced Technology Marine Systems Association for Geographic Information B Ae Sema Ltd. Berkshire County Council British Telecommunications plc CAM Ltd. Cambridgeshire County Council Digital Equipment Co Ltd. Institute of Terrestrial Ecology Lase
5、r Scan Ltd. Local Government Management Board Logica UK Ltd. London Fire and Civil Defence Authority Ministry of Defence Ordnance Survey Royal Engineers Survey Royal Institution of Chartered Surveyors University of Edinburgh Amendments issued since publication Amd. No.DateComments 8918January 1996In
6、dicated by a sideline in the margin Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 BSI 09-1999i Contents Page Committees responsibleInside front cover Forewordii Section 1. General 1.1Scope1 1.2
7、Normative references1 1.3Definitions1 1.4Editorial conventions particular to this Part of BS 75671 Section 2. Physical file structure 2.1Physical media2 2.2Volume structure2 2.3Volume termination record2 2.4Physical block size2 2.5Physical record size2 Section 3. Physical record structure of plain N
8、TF 3.1Records3 3.2Fields3 3.3Example4 Section 4. Record implementation 4.1Additional records5 4.2Records common to all levels6 4.3Records for levels 1 and 211 4.4Records for level 315 4.5Records for level 421 4.6Records for level 524 Annex A (informative) Summary list of record descriptors27 Annex B
9、 (informative) Example of level 2 data transfer28 List of referencesInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 ii BSI 09-1999 Foreword This Part of BS 7567 has been prepare
10、d under the direction of the Information Systems Technology Standards Policy Committee. BS 7567-2:1992 specifies how NTF, a data transfer standard for a wide range of geographic data, is encoded using plain NTF which is a set of formatting instructions designed specifically for this type of data. BS
11、 7567-3:1992 may be used as an alternative to this Part by agreement between the donor and recipient. It is essential for users of this Part to refer to Part 1 of BS 7567. In section 4, various subclauses are introduced but not used: this device is for the convenience of cross-referral between the i
12、mplementation specifications for NTF levels 3 and 4. For example, a record for level 3 implemented in 4.4.6 is implemented for level 4 at 4.5.6. Section 4 in this Part corresponds exactly to section 4 of BS 7567-1:1992. For example, the record implementation specified at 4.4.6 of this Part has its s
13、yntax specified in 4.4.6 of Part 1. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summa
14、ry of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 40, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside fr
15、ont cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 BSI 09-19991 Section 1. General 1.1 Scope This Part of BS 7567 specifies the procedures for the formatting of NTF Data Models, the inter
16、change file structures and the detailed record interpretations specified in Part 1 of BS 7567:1992 in accordance with detailed instructions fully specified herein. NOTESyntax is also specified for a minority of records which are implemented differently when plain NTF is used instead of BS 6690. 1.2
17、Normative references This Part of BS 7567 incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside of the back cover. Subsequent amendments to, or revi
18、sions of, any of these publications apply to this Part of BS 7567 only when incorporated in it by updating or revision. 1.3 Definitions For the purposes of this Part of BS 7567, the definitions given in 1.3 of BS 7567-1:1992 apply together with the following. 1.3.1 plain NTF the custom-designed form
19、atting instructions for NTF specified in BS 7567-2:1992 1.4 Editorial conventions particular to this Part of BS 7567 1.4.1 For the purposes of BS 7567-2:1992, the editorial conventions in 1.4 of BS 7567-1:1992 shall apply. 1.4.2 Use of | This character is used to signify a space in examples of NTF d
20、ata. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 2 BSI 09-1999 Section 2. Physical file structure 2.1 Physical media 2.1.1 inch tape Unless the donor and recipient agree to an alternative med
21、ium, the transfer shall be made on unformatted inch 9-track tape with the 8-bit data written at a density of 1600 bpi. Header and trailer records (other than those internal to plain NTF) shall not be used, that is, the tape is unlabelled. The final block on each tape shall be followed by a single ta
22、pe mark. 2.1.2 Formatted media If donor and recipient agree to use formatted media, the NTF file shall be written to (or stored on) logically formatted media such as hard disk, floppy disk or logically formatted tape (for example, a inch cartridge written using the UNIX tar command), then the follow
23、ing shall also apply: a) The end of record character EOR shall not be one that is commonly used for carriage control; NOTEAny control character is liable to special interpretation. It is recommended that the EOR character be a printing character that does not normally appear in data text strings or
24、NTF control records. For example, a %. b) Each physical record shall be followed by the carriage control character(s) for the operating system the NTF file is written under. Thus, on a UNIX system each physical record shall end: . . . CONT_REC EOR and on an MS/DOS system the physical record shall en
25、d: . . . CONT_REC EOR where represents “carriage-return” and represents “line-feed”. c) NTF disk files that are not generated for direct transfer to raw tape shall not have any logical blocks within them. NOTEFile transfer between systems may cause expansion/contraction of carriage control character
26、s. This changes the number of characters in the block and upsets any block reading mechanism. 2.2 Volume structure If the size of the transfer set exceeds the size of the physical volume, it shall be extended to additional volumes. A volume shall start with an NTF volume header record and terminate
27、with an NTF volume termination record. When writing data, the donor shall ensure that there is enough space to complete a logical record on the current volume. NOTE 1A volume is normally associated with one unit of dismountable physical media. For example, a magnetic tape. NOTE 2The existence of mor
28、e than one volume has no influence on the organization of the data, except that a logical record cannot be continued across volumes. 2.3 Volume termination record This record shall end both single volumes and complete transfer sets. A field shall indicate continuation or completion of the transfer s
29、et. 2.4 Physical block size Unless the donor and recipient agree to an alternative the block size shall be 2000 characters for transfers on unformatted media. 2.5 Physical record size Unless the donor and recipient agree to use a fixed length of 80 characters, physical records shall be of variable l
30、ength with a maximum 80 characters. If fixed length records are used, the donor shall pack as many data fields as possible into the record. Continuation records shall be used when a logical record exceeds the maximum length of a physical record. NOTE 1Variable length records are created by the donor
31、 and not by the tape facilities of a particular computer system. NOTE 2Records are identified within a fixed length block of 2000 characters by an end of record character. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy
32、, (c) BSI BS 7567-2:1992 BSI 09-19993 Section 3. Physical record structure of plain NTF 3.1.1 Record descriptor All records (except a null record, see 3.1.6) shall start with a specified two character field (format A2) which indicates the purpose of the record. The characters are a code matched to t
33、he name of the record specified in section 4 of BS 7567-1:1992. Records shall have the format specified at a particular NTF level associated with this descriptor or one defined in a data dictionary in the case of level 5. A correspondence table for record descriptors and record names is provided at
34、Annex A. NOTEAll default record descriptors can be interpreted as two digit numbers. This is an obligatory one-character field in all records except volume terminator and null records, and shall occur immediately in front of EOR in any physical record. It shall be 0 (no continuation) or 1 (logical r
35、ecord continues). (See also 3.1.4) The last character in a record (variable and fixed) shall always be the record terminator, “end of record”. This character shall be defined in the volume header record. The default value shall be (carriage return) for unformatted media and % (percent) for formatted
36、 media. (See also 2.1.) 3.1.4 Continuation record Where a logical record exceeds 80 characters, the record shall extend into continuation records in the next physical record. In such a case, the continuation mark in the preceding physical record shall be set to 1. 3.1.5 Splitting records Where NTF r
37、ecords are written to unformatted media, these shall not be split across blocks, though a continuation record may start in the next block. Null records, consisting entirely of SPCS shall be used to fill blocks. These may be of any length. NOTEIf the penultimate character position in a block is a rec
38、ord terminator, then the next character will also be a record terminator. 3.1.6 Null records (block filling) Where NTF fields are written to unformatted media, these shall not be split across physical records and blocks and therefore block filling is required when variable length physical records ar
39、e written to unformatted media. A null record comprising SPC characters shall be used to fill the remaining block space after the last meaningful field. Several such records may be used, each one terminating with EOR. NOTE 1The first appearance of a null record in a block effectively means that the
40、block contains no more data. NOTE 2When the fixed length record option is being used, the last block on a tape will probably require null records to complete it. 3.2 Fields 3.2.1 Splitting fields Fixed length fields shall not be broken when continuation records are being used. Certain variable lengt
41、h text fields may continue into continuation records, and may also cross blocks. These fields may be split at any convenient point. Unless donor and recipient agree to use a different character the divider for variable fields shall be . Dividers shall terminate all variable length TEXT fields. NOTE
42、1This character is defined in the volume header record and is only used to terminate variable length text fields. NOTE 2FREE_TEXT fields in such records as comment, database quality, section quality and volume terminator are not terminated by dividers. 3.2.3 Field descriptors In interpreting the enc
43、oding of a “real” field descriptor, Rn,d, the decimal point is not output. Thus the real number2.75, output using the field descriptor R4, 2, would appear as0275. 3.1 Records REC_DESC 3.1.2 Continuation markCONT_MARK 3.1.3 Record terminatorEOR 3.2.2 Field dividerDIVIDER Licensed Copy: London South B
44、ank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 4 BSI 09-1999 3.2.4 Count fields Plain NTF shall use additional count fields to indicate the number of times a field repeats and the number of characters in a TEXT field. The v
45、alue stored in a count field shall always be greater than zero. NOTECount fields are named NUM_something. Their format is defined as size where size is the size of the field containing the count. 3.3 Example Examples of plain NTF record and field structure are provided in Annex B. Licensed Copy: Lon
46、don South Bank University, London South Bank University, Fri Dec 08 10:26:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7567-2:1992 BSI 09-19995 Section 4. Record implementation 4.1 Additional records 4.1.1 General This clause specifies extra physical records that are necessary for the implementa
47、tion of plain NTF and are relevant at all levels: 1) CONTREC, the continuation record 2) Null record, the block fill requirements 3) VOLTERM, the volume termination record 4.1.2.1 Record specification Logical records shall not be continued from one section to the next. 4.1.2.2 Description a) To tran
48、sfer further fields when a logical record is longer than a single physical record. b) A continuation record may be associated with any record except volume terminator, comment and null, and it assumes a structure appropriate to the logical record. c) The character before EOR in any physical record (
49、except for the volume terminator and null records) is always a continuation mark CONT_MARK. When a record would otherwise be longer than 80 characters a record may be continued by appropriate use of the continuation mark and continuation records. d) With the exception of fields which are of variable length, for example, TEXT, fields are not broken across records. If there is insufficient space remaining in a physical record to accommodate a field, the record is terminated and the field continued with the (next) continuation re
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