SPSS SAV DSC

The SPSS SAV DSC reads data from, and writes data to, an SPSS *.sav file. It has these features:

Feature	UNICOM Intelligence database
Storage type	Single file
Read	Yes
Write/update	Yes
Unbounded loops (levels)	No
Native WHERE clause support	No
Compressed format	No
Multiple user read	Yes
Multiple user write	No

The SPSS SAV DSC stores data in an SPSS *.sav file by using the SPSS I/O DLL. For more information about how UNICOM Intelligence data is written to a *.sav file, see Writing to an SPSS Statistics .sav file.

skidemo	UNICOM Intelligence database	UNICOM Intelligence file	Quantum	Quanvert	SPSS
Total size	19	2.18	0.9	3.25	1.7
Backup	18.1	0.65	*	2	*

Similar to the Quantum CDSC, the SAV format is not suited for large, sparsely populated data sets. However, the SPSS SAV DSC has an acceptable storage size for small to medium sized data sets.

The following table provides the SPSS SAV DSC read performance (measured in seconds):

skidemo	UNICOM Intelligence database	UNICOM Intelligence file	Quantum	Quanvert	SPSS
1 variable	0.062	0.062	0.109	0.031	0.062
5 variables	0.11	0.063	0.204	0.078	0.078
All variables	1.078	0.562	0.843	0.672	0.61

▪The SPSS SAV DSC has acceptable read performance for the entire data set, which makes it a suitable input data format for data management activities.

▪In SPSS SAV DSC has acceptable single variable read performance for ad hoc tabulation scenarios.

The following table provides SPSS SAV DSC write performance (measured in records per second):

skidemo	UNICOM Intelligence database	UNICOM Intelligence file	Quantum	Quanvert	SPSS
Records per second	80	1897	1523	*	1971

The following table provides update performance (measured in seconds) for every value in a single weight column:

skidemo	UNICOM Intelligence database	UNICOM Intelligence file	Quantum	Quanvert	SPSS
1 variable	0.719	0.219	0.282	*	0.578

▪The SPSS SAV DSC has excellent write performance when exporting to the *.sav file format.

▪The SPSS SAV DSC has acceptable update performance when used with small to medium sized data sets. Update performance is poor against larger data sets.

▪Data export to other formats. The SPSS SAV DSC has acceptable read performance for exporting to other DSCs.

▪Tabulation. The SPSS SAV DSC has acceptable performance when used for most tabulation scenarios.

▪Portable data format. The SPSS *.sav format is supported by UNICOM Intelligence, IBM SPSS, and some other third-party products. Support across the different product suites, and the relatively small storage size, makes *.sav files a good portable data format.

▪Low-volume, single-user data collection. While not suitable for higher-volume data collection (>1000 cases), the SPSS SAV DSC can be used for disconnected UNICOM Intelligence applications, such as CAPI or Data Entry.

▪Data management. Although copying data to the SPSS SAV DSC is fast, the DSC exhibits poor performance when updating variables. This means that the creation of weights, and the addition of coded values, can be slow when using the SPSS SAV DSC. The poor update performance is due to the SPSS SAV DSC having to rewrite the entire *.sav file each time weights are created, or each time an UPDATE statement is run.

▪Unbounded levels data. The SPSS SAV DSC does not support unbounded loops and cannot be used to store levels data.

▪Disabling scan for categories. By default, the SPSS SAV DSC scans the entire data set to find extra values that are not defined as categories. The scan process can be time-consuming for large data sets and can be disabled by creating an *.ini file for the *.sav file that includes the following line:

Note The ScanForCategories setting forces the SPSS SAV DSC to silently ignore any unlabeled values in the case data.

▪Generating metadata in advance. When you do not use an .mdd file, the SPSS SAV DSC generates an MDM document, that contains many variables, for the .sav file. The MDM generation process can take quite a long time. To improve load times in UNICOM Intelligence Survey Tabulation and UNICOM Intelligence Reporter, it is recommended that an .mdd file is created for the .sav file in advance.